Bhagya – Page 54 – PSEB Solutions

PSEB 10th Class Science Notes Chapter 15 Our Environment

December 21, 2024December 20, 2024 by Bhagya

This PSEB 10th Class Science Notes Chapter 15 Our Environment will help you in revision during exams.

PSEB 10th Class Science Notes Chapter 15 Our Environment

→ A biotic community survives in an environment entirely by materials and energy provided by its environment.

→ The environment is the sum total of all external conditions and influences that affect the life and development of an organism, i.e., the environment includes all the physical or abiotic and biological or biotic factors.

→ The ecosystem is defined as the interaction between the physical environment and the biotic community.

→ An ecosystem is a unit of the environment that can be identified and studied. The term ‘Ecosystem’ was coined by Sir Arthur Tansley (1935).

→ The various components of an ecosystem are interdependent.

→ An ecosystem can be natural or artificial, small or large, and temporary or stable. An ecosystem has a defined organization having two structural components i. e. biotic and abiotic.

→ The ecosystem may vary in sizes such as a small pond or a large forest or ocean.

→ Two major categories of ecosystems are terrestrial and aquatic ecosystems.

→ Its functional components include the volume and rate at which materials circulate and energy flow as well as the process of interaction between biotic and abiotic components.

→ The biotic components of any natural ecosystem comprise

producers
consumers (primary and secondary)
decomposers.

→ Both materials and energy enter the living world through the producers.

→ There is always a unidirectional flow of energy in a food chain.

→ We have an impact on our environment.

→ Different materials are cycled in the environment in separate biogeochemical cycles.

→ In these cycles, essential nutrients change from one form to another.

→ Enzymes are always specific in their action.

→ Plastic can neither be decayed by micro-organisms nor by other dead organisms.

→ Those substances which can be decayed by micro-organisms are called biodegradable substances. And those which cannot be decayed are known as non-biodegradable substances.

→ The organisms like plants, animals, micro-organisms, human beings, and their physical surroundings interact with each other. They maintain a balance in nature.

→ Forest, ponds, and waterfalls are examples of natural ecosystems whereas gardens and fields are man-made artificial ecosystem.

→ All green plants and blue-green algae are called producers because they trap sunlight and prepare their own food.

→ All organisms directly or indirectly are dependent on producers for their survival.

→ Those organisms which are dependent on producers for food are called consumers.

→ Consumers mainly are of three types: herbivores, carnivores, or omnivores.

→ Various organisms are linked together for their food requirements and form a food chain.

→ Each step of a food chain forms a trophic level.

→ Autotrophs trap solar energy and transform it into chemical energy.

→ The green plants in the terrestrial ecosystems capture about 1% of the energy of sunlight and convert it into food energy.

→ Primary consumers change almost 10% of consumed food into organic matter.

→ A food chain basically consists of three or four levels.

→ The length and compressibility of food chains vary greatly.

→ Instead of a straight-line food chain, a branched relationship is developed. This branched-chain forms a web called a food web.

→ Many chemicals mix with soil and enter water bodies and become part of the food chain.

→ Non-biodegradable substances accumulate in our body which is called Bio-magnification.

→ The ozone layer protects us from ultraviolet rays coming from the sun towards the earth.

→ At higher levels of the atmosphere ozone (O₃) is a product of UV radiation acting on oxygen (O₂) molecules.

→ Chemicals like chlorofluorocarbons (CFCs) are responsible for the depletion of the ozone layer.

→ Improvements in our lifestyle have resulted in a greater amount of garbage.

→ Acid rain is the result of air pollution.

→ Global warming is due to the slow rise in the earth’s temperature due to an increase of CO₂ concentration in the atmosphere.

→ Global warming can be stopped by cutting down the use of fossil fuels.

→ Wastes are of two types i.e. biodegradable and non-biodegradable waste.

→ WHO (World Health Organisation) has defined solid waste as “a matter in the wrong place i.e., a non-liquid, no-gaseous substance no longer useful to the holder.”

→ Solid Waste is a by-product of human development and growth.

→ Approximately every resident of urban India generates about 500 g of solid waste.

Its generation is directly proportional to sources of income. Higher the income – greater is the consumption and bigger is the waste.

→ Solid waste is a heterogeneous mixture and may have different types of components.

→ Collection, treatment, and disposal of waste are important aspects requiring urgent consideration.

→ Modes of disposal of wastes are:

Landfills: It is the method used in urban areas to bury the solid waste in low-lying areas to level the uneven ground.
Recycling: It is the method of recovery and processing of biodegradable wastes or materials after they have been used, which enables them to be reused.
Composting: In this method, domestic waste like fruit and vegetable waste, left-over food, leaves of potted plants, etc., can be converted into compost and used as manure.
Incineration: It means ‘reduction to ashes’. The burning of a substance at a high temperature to form ash is called incineration. It is used to destroy household waste, chemical waste, and biological waste. Incineration is carried out in an incinerator.

→ Ecosystem: The interchange of energy and matter between biotic and abiotic components is called an ecosystem.

→ Biome: When ecosystems combine, a larger system is formed which is called a Biome.

→ Biosphere: When all the biomes of the world combine together resulting in a large unit it is termed as the biosphere. It is considered to be the largest biological system.

→ Hydrosphere: The part of Earth covered with water is called the hydrosphere.

→ Lithosphere: The outer crust of our planet Earth is called the lithosphere.

→ Atmosphere: The multi-layered gaseous envelope of air that covers the whole of our planet Earth like a blanket is termed as atmosphere.

→ Consumer: Those organisms which cannot produce their own food and consume already formed food are called consumers.

→ Nutrition: Nutrition is the process of providing or receiving nourishing substances with the help of the food chain.

→ Food chain: A chain formed by producers, consumers, and decomposers is called a food chain. It is a series of organisms feeding on one another at various biotic levels.

→ Food web: The network of overlapping food chains is called the food web.

→ Biogeochemical cycle: A constant interaction between the biotic and abiotic components of the biosphere makes it a dynamic but stable system. These interactions consist of a transfer of matter and energy between the different components of the biosphere.

→ Macronutrients: The nutrients which are required in large amounts by the body are called macronutrients, e.g. H, N, C, O, P.

→ Micronutrients: The nutrients which are required in small amounts by the body are called micronutrients, e.g. Mn, Zn, Cu, etc.

→ Water cycle: The whole process in which water evaporates and falls on the land as rain and water flow back into the sea via rivers is known as the water cycle.

→ Primary Consumers: Those organisms which eat plants or their products are known as herbivores or primary consumers.

→ Secondary consumers: Those organisms which eat the flesh of other animals are known as carnivores or secondary consumers.

→ Flora: The population of plants and trees in a region.

→ Fauna: The animal population of a region.

→ Community: Group of plants and animals living together e.g. plants and animals living in a pond.

→ Bio-magnification: Accumulation of non-biodegradable substances in large amounts in our body is called bio-magnification.

→ Biodegradable substances: Those substances which are broken down into simple substances by the decomposers in the life cycle are called biodegradable substances.

→ Non-biodegradable substances: Those substances which cannot be decayed by decomposers are called non-biodegradable substances.

→ Environment: Living organisms and their surroundings constitute the environment.

→ Ecology: It is a branch of science which deals with the relationship between living organisms and their environment on the basis of living and non-living components.

→ Components of Ecosystem: Physical, chemical, and living parts that form the ecosystem are called the components of the ecosystem.

→ Biogeochemical cycle: The constant interaction between biotic and abiotic components of the biosphere makes it a dynamic but stable system. These interactions consist of a transfer of matter and energy between different components of the biosphere.

→ Biological Magnification: The successive increase in the concentration of some toxic substances through different trophic levels of a food chain is called biological magnification.

→ Producer: Those plants and animals which convert solar energy into chemical energy and prepare their own food are called producers.

→ Decomposer: Those organisms which break down complex organic compounds from the surface of their bodies and convert them into simple inorganic substances with the help of enzymes are called decomposers.

→ Herbivores: Organisms that consume only plants and their products as food is called Herbivores.

→ Carnivores: Organisms which eat the flesh of other animals for survival are called carnivores.

→ Omnivores: Organisms that eat plants, animals, and their products are called omnivores.

→ Food Web: Branched food chain is called a food web.

→ Ozone layer: The layer of ozone in the stratosphere is called as ozone layer.

→ Garbage: The waste accumulated by common domestic and agricultural activities is known as garbage.

PSEB 9th Class Science Important Questions Chapter 10 Gravitation

December 21, 2024December 20, 2024 by Bhagya

Punjab State Board PSEB 9th Class Science Important Questions Chapter 10 Gravitation Important Questions and Answers.

PSEB 9th Class Science Important Questions Chapter 10 Gravitation

Long Answer Type Questions:

Question 1.
Define Newton’s universal law of gravitation and establish mathematical formula for force of attraction between two objects.
Answer:
Newton’s universal law of gravitation-Every particle in this universe attracts each and every particle, the force of attraction is:
1. directly proportional to the product of both the masses.
2. Inversely proportional of the square of the distance between the two. This force always acts along the line joining the two masses.
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 1
Derivation of Mathematical Formula: From the fig. Jet there are two balls A and B having masses m₁ and m₂ distance between them is ‘r’.
According to Newton’s third law of motion ball A exerts a force FAB on the ball B and ball B exerts a force FBA on the ball A. These forces are equal and opposite
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 2
where G is universal gravitational constant. This is named so since its numerical value remains constant in whole of the universe and the formula is known as Newton’s universal law’ of gravitation.
Value of G
G = 6.67 × 10^-11 Nm²/kg²

Question 2.
Write Kepler’s law in context with the motion of planets.
Answer:
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 3
By the 16th centuary, a lot of data on the motion of planets had been collected by many astronomers. Johannes Kepler derived three law s based on these data. These are known as Kepler’s laws. These are:
1. Law of orbits (First laws): The orbit of a planet is an ellipse and the sun is at one of the foci, as shown in fig. In this fig. Sun is shown at O.

2. Law of area (Second laws): The line joining the planet and sun sweep equal areas in equal interv als of time. Thus, time taken for the motion from A to B is same as for the motion from C to D and area OAB and OCD are equal.

3. Law of time period (Third law): The cube of mean distance of a planet from the sun is directly proportional to square of its orbital time period
T² ∝ r³
But Kepler could not give a theory which explained the motion of planets.
Newton showed that due to motion of planets sun exerts force of gravtation on them.
i.e. T²/r³ = constant.

Question 3.
How did Robert Boyle proved experimentally that all bodies fall in vacuum with same acceleration?
Or
How did Robert Boyle show experimentally that a coin and a piece of paper when dropped simultaneously from same height in vacuum fall with same acceleration?
Answer:
Boyle’s Experiment: As shown in fig. Robert Boyle took a long glass tube. A heavy coin and a piece of paper were placed inside the tube. The ends of the tube were closed. Air from the tube was removed with the help of a vacuum pump.
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 4
When the tube was quickly inverted it was seen that coin and a piece of paper hit the bottom of the tube at the same time. Now the experiment was repeated with air inside the glass tube. This time it was observed that a piece of paper falls slowly whereas the coin immediately hit the bottom of glass tube. This experiment proves that in vacuum all bodies irrespective of their masses (both light and heavy) fall towards earth with same acceleration

Question 4.
(a) Prove that acceleration due to gravity is independent of mass.
(b) Find the value of ‘g’.
Answer:
(a) Consider a body of mass ‘m’ lying on the surface of earth. Suppose M and R are respectively mass and radius of earth.
Let F be the force of gravity acting on the body
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 5
This acceleration is called acceleration due to gravity
∴ g = $\frac{G M}{R^{2}}$
This equation is free from mass ‘m’. This shows that due to force of gravity the acceleration produced in an object is independent of its mass.

(b) To find the value of ‘g’
G = 6.67 × 10 “n Nm2/kg2
R = 6400 km
= 6400 × 1000 m
= 64 × 105 m
= 6.4 × 106 m
Mass of the earth(M) = 6 × 1024 kg
But g = $\frac{G M}{R^{2}}$
= $\frac{6.67 \times 10^{-11} \times 6 \times 10^{24}}{\left(6.4 \times 10^{6}\right)^{2}}$
or g = 9.8 ms^-2

Question 5.
Describe those factors which are responsible for variation in the value of acceleration due to gravity ‘g’?
Answer:
Variation in the value of acceleration due to following factors:
Variation in g with altitude-Value of ‘g’ is maximum on the surface of earth. As we move in the upward direction (higher altitudes) value of ‘g’ goes on decreasing. We can calculate value of ‘g at altitude using mathematical formula. If
g_e = acceleration due to gravity on the surface of earth
g_h = acceleration due to gravity at height h
R = radius of earth
we know g_h = g_e$\left[\frac{\mathrm{R}^{2}}{(\mathrm{R}+h)^{2}}\right]$
If we know value of h, we can calculate g_h.
Special case-If ‘h’ is half the value of radius of earth i.e. h = $\frac {R}{2}$ then
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 6
Another interesting fact that value of ‘g’ is zero at the centre of earth.

2. Variation in g due to shape of earth-
Earth is not exactly spherical. It is somewhat egg-shaped. Its radius at poles is less than that at equator as shown in fig.
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 7
As shown in fig. radius of earth at equator is 6378 km and radius of earth at poles is 6357 km. Thus, value of g at poles is g_p = 9.831 m s_-2 (maximum) and minimum value at equator is g_e = 9.782 m s_-2. We use average value of g calculated from g_e, and g_p.

3. Effect of depth: If we go deep under the earth e.g. in caves or in mines, value of ‘g’ i’ decreased. Value of g goes on decreasing, if depth goes on increasing. At the centre of earth, value of g is zero.
$\frac{\mathrm{W}_{d}}{\mathrm{~W}_{e}}=\frac{g_{d}}{g_{e}}=\left[1-\frac{d}{\mathrm{R}}\right]$

Question 6.
Establish the relation between ‘g’ and ‘G’.
Or
Deduce an expression for it in terms of mass of the earth ‘M’ and universal gravitational constant ‘G’.
Or
Show that the acceleration due to gravity of an object is independent of its mass.
Answer:
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 8
Relation between ‘g’ and ‘G’. Suppose the earth is a sphere of mass M and radius R, Consider a body of mass m lying at a distance ‘r’ from the centre of the earth. According to Newton’s law of gravitation, the force of attraction between the earth and the body,
F = $\frac{\mathrm{GM} m}{r^{2}}$ ……………… (i)
Tills force of gravity produces an acceleration ‘g’, is the body of mass m.
Hence, from Newton’s second law,
F = Mass × Acceleration
F = m × g ……………..(ii)
From equations (i) and (ii) we get
mg = $\frac{\mathrm{GM} m}{r^{2}}$
or g = $\frac{\mathrm{GM}}{r^{2}}$ ………..(iii)
This equation gives relation between acceleration due to gravity ‘g’ at points far away from the earth and gravitational constant ‘G’.
Since (3) does not involve’m’ it is therefore eviden t that ‘g’ does not depend upon the mass of the body.

Question 7.
What is Archimedes principle? How can you verify it experimentally? Also write applications of Archimedes principle.
Answer:
Archimedes Principle: According to this principle when a solid body is immersed either completely or partially in a liquid, it experiences an upward thrust which is equal to the weight of the liquid displaced by the immersed part of the body.”

Experimental Verification: Take a stone piece and tie it to the hook of a spring balance. Hold the spring balance in your hand or support it from the stand so as to suspend the stone piece as shown in fig.
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 9
Note, the reading on the spring balance to know the weight of the stone. Now pour some water a beaker with and slowly immerse the stone in the water while remaining tied with the hook of spring balance as shown in fig. (b). You will see that spring balance shows a decreased reading i.e. weight of stone is decreased after it is immersed in the water.

Subtract the two readings to know the decrease in the weight of stone. As soon as the stone is immersed in the water it displaces water equal to its own volume. Collect this water in other beaker and measure its weight. You will find that this weight of water is equal to the decrease of weight of the stone. Thus Archimedes principle is proved.

Applications of Archimedes’ Principle:

Archimedes principle is used in designing ships and submarines.
Lactometers are constructed on Archimedes’ Principle which are used to measure puritv of a sample of milk.
Hydrometers used to measure density of liquid are also based on Archimedes principle.

Short Answer Type Questions:

Question 1.
Which one is greater-the gravitational force of the earth on 1 kg iron or the force of gravitation applied by 1 kg on earth?
Answer:
According to Newton’s law of Gravitation there exists of mutual force of attraction between two objects. Since the mass of iron is less than the mass of the earth, therefore earth attracts 1 kg mass towards it with a greater force which is noticeable.

Question 2.
Why is G called universal gravitational constant?
Answer:
G is called universal gravitational constant because its numerical value is same in the whole universe. This value is G = 6.67 x 10^-11 Nm²/kg².

Question 3.
Is the value of ‘g’ at a given place same for different bodies or it is variable?
Answer:
From the relation between the acceleration due to gravity ‘g’ and universal gravitational constant G, we know g = $\frac{\mathrm{GM}}{\mathrm{R}^{2}}$
From this equation it is evident that the value of ‘g’ does not depend upon the mass of the body. Thus we reach a conclusion that at a given place the value of g is same for different bodies.

Question 4.
Why does a body becomes weightless at the centre of earth?
Answer:
We know value of g goes on decreasing as we continue moving deep into the earth and value of acceleration due to gravity (g) = 0 at the centre of earth. Thus, a body whose mass is m,
Weight of body = m × 0 = 0
Therefore, body becomes weightless.

Question 5.
A tennis ball jumps higher at hills than at planes. Explain.
Answer:
Value of g decreases with altitude, thus gravitational force acting on ball at hills is less as a result ball jumps higher at hills than at planes.

Question 6.
The weight of an object on the surface of earth is 9.8 N. What does this statement mean?
Answer:
We know that value of ‘g’ on the surface of earth is 9.8 m/s² and the relation for weight of an object is:
w = m × g
9.8 = m × 9.8
or m = $\frac {9.8}{9.8}$
∴ m = 1 kg
The given statement therefore means the mass of the object on earth is 1 kg.

Question 7.
What type of motion a freely falling body execute under gravity?
Answer:
A body falling freely under gravity executes uniform accelerated motion. If bodies with different masses and different shapes are allowed to fall freely in vacuum, they all will have same acceleration due to gravity.

Question 8.
Give points of difference between Acceleration due to gravity (g) and Universal gravitational constant'(G).
Answer:
Difference between g and G:

Acceleration due to gravity (g)	Gravitational constant (G)
1. It represents acceleration acquired by the body due to gravity.	It represents force of attraction between two masses of 1 kg each lying 1 m apart.
2. Its value is different at different places on earth surface.	Its value is constant at all places. Thus, it is called universal constant.
3. Its value at the surface of earth is 9.8 m/s².	Its value is 9.67 × 10^-11 Nm²kg^-2.
4. It is a vector quantity.	It is a scalar quantity.

Question 9.
You buy W weight of sugar at a place situated on equitorial line and then take it to Antarctica. Will that sugar weigh same there? If not whether it would be more or less.
Answer:
The value of ‘g’ at Antarctica is not same as on equator. The value of ‘g’ increases on Antarctica therefore, sugar bought at any place on equitorial line when taken to Antarctica would have more weight but its mass will remain the same because mass is a constant quantity.

Question 10.
Why cannot we move a finger without disturbing all the stars?
Answer:
When we move our finger, then distance between finger and all other things in the universe change and as a result force of gravitation also changes. Thus, all the things get disturbed, although this disturbance is negligible.

Question 11.
Distinguish between Gravitation and Gravity.
Answer:

Gravitation: Gravitation is the force of attraction between any two bodies in the universe. The attraction between the sun and the earth, the attraction between a table and a chair are examples of gravitation.
Gravity: Gravity is a special case of gravitation when one of the two bodies is the earth. Gravity is the attraction between the earth and any object lying on or near its surface. A ball thrown upward falls back on the surface of the earth due to earth’s force of gravity.

Question 12.
Explain why a small piece of stone is not attracted towards another big place of stone on the earth’s surface?
Answer:
Because of very small value of G, the force of attraction between any two such ordinary sized bodies is so small that it cannot produce motion in them.

Question 13.
The earth attracts an apple. Does the apple also attract with earth? If it does, why does the earth not move towards the apple?
Answer:
The apple also attracts the earth with an equal and opposite force. The mass of the earth is very large compared to that of apple. So, the acceleration produced in earth is very small as compared to that in the apple. Hence, the motion of the earth towards the apple is not appreciable and therefore, is not noticeable.

Question 14.
If the force of gravity somehow vanishes today, why would we be sent being in space?
Answer:
In the absence of force of gravity, the centripetal force required to keep us rotating along the earth would not be available. As a result would fly off along the tangent to with into the space.

Question 15.
What is meant by density and relative density?
Answer:
Density of a substance is defined as the mass of a substance contained in a unit volume.
Density = $\frac{\text { Mass }}{\text { Volume }}$
Its SI unit is kg m^-3.

Relative density or specific gravity is the ratio of density of substance to the density of same volume of water
R.D or S.G = $\frac{\text { Density of substance }}{\text { Density of water }}$

Density of water is 1,000 kg m^-3 in SI.
According to Archimedes’ principle, when a body is immersed in water, the loss of weight in water is equal to the weight of an equal volume of water, i.e., weight of water displaced. Hence R.D. can be written as
R.D = $\frac{\text { Weight of substance }}{\text { Loss of weight of body in water }}$

Question 16.
What do you mean by buoyancy and centre of buoyancy? In which direction does the buoyant force on an object immersed in a liquid act?
Answer:
Buoyancy: When a body is immersed partially or wholly in a fluid (liquid or gas), it displaces fluid. The displaced fluid exerts an upward force on the body.

The upward force acting on a body imnu rsed in a fluid is called upthrust or force of buoyancy and the phenomenon is called buoyancy. The buoyancy acts through the centre of gravity of the displaced fluid which is called centre of buoyancy.

Question 17.
State Archimedes’ principle.
Answer:
Archimedes’ Principle. When a solid body is immersed completely or partially in a fluid, it experiences an upward thrust which is equal to the weight of the fluid displaced by the immersed part of the body.

Question 18.
Name two forces which act on a body immersed in a liquid. Give the directions in which they act.
Answer:
Two forces which act on a body immersed in a liquid are:

Weight of the body acting downward.
An upthrust due to displaced liquid.

Question 19.
How is submarine able to move on water surface as well as go under water?
Answer:
To move submarine under water, water is pumped in its special tanks. This causes a net increase in weight and thus submarine goes down in water.

To bring the submarine upon the surface of sea, the water from the tanks is thrown out by pumps. When water from the tanks of submarine is taken out, the net weight of the submarine decreases without any change in its volume and it comes up on the surface of water.

Question 20.
Give reason when Big buildings and dams have wide foundations for safety.
Answer:
Dams and big buildings have wide foundations for safety, because they may not collapse under high pressure of the building.

Question 21.
A steel needle sinks in water but a steel ship floats. Explain how?
Answer:
A steel needle sinks in water because it displaces less weight of water which provides less buoyant force than the actual weight of the needle. On the other hand, steel ship floats because it displaces a large weight of water which provides a greater buoyant force to keep it a float.

Question 22.
Give reasons for the following :
(a) A sharp blade is more effective in cutting an object than a blunt blade.
(b) A cork piece floats but an iron piece sinks in water.
Answer:
(a) We know Pressure = $\frac{\text { Thrust }}{\text { Area }}$. For the given thrust, pressure ∝ $\frac{\text { 1 }}{\text { Area }}$. Thus the effect of the same magnitude of force is more when the area of surface in contact is less. Hence a sharp blade is more effective in cutting an object than a blunt blade.
(b) The density of the cork piece is less than the density of water, and the. density of the iron piece is more than the density of water. Hence, the cork piece floats but the iron piece sinks in water.

Question 23.
Explain the following:
(a) Swimmers are provided with an inflated rubber jacket.
(b) It is easier of swim in sea water than in river water.
Answer:
(a) Swimmers are provided with an inflated rubber jacket to increase the volume such that density is decreased, which is helpful for swimming.
(b) It is easier to swim in sea water than in river water because density of sea water is more than water of the needle sinks in a river while a ship float on it.

Question 24.
Why is the pressure on ground more when a man is walking than when he is standing?
Answer:
When the man stands he exerts a force on the ground equal to his own weight. But when he walks, he pushes the ground backward and exerts an additional force on the ground. That is why pressure on the ground is more when a man is walking than when he is standing.

Question 25.
Why a bucket of water is lighter when in water than when it is taken out of water?
Answer:
Inside water, the bucket experiences upthrust exerted by displaced water, so its apparent weight becomes less than the actual weight. When bucket is taken out of water, upthrust on the bucket disappears and it feels heavier.

Question 26.
If a fresh egg is put into a beaker filled with water, it sinks. On dissolving a lot of salt in the water, the egg begins to rise and floats. Why?
Answer:
The average density of a fresh egg is more than that of pure water but less than that water in which salt is dissolved. So a fresh egg sinks in pure water while it floats in salty water.

Important Formulae:

F = G$\frac{\mathrm{M} m}{\mathrm{R}^{2}}$
F = mg
g = G$\frac{\mathrm{M}}{\mathrm{R}^{2}}$
υ = u +gt
υ² = u² + 2gh
h = ut + $\frac {1}{2}$gt²
g_m = $\frac {1}{6}$g_e
(g_m = Acceleration due to gravity on moon , g_e = Acceleration due to gravity on earth)

Necessary Data-
Earth
Mass = 6 × 10²⁴ Kg
Radius = 6.4 × 10⁶ m (6400 Km)
Distance from Sun = 1.5 × 10¹¹ m
Moon
Mass = 7.3 × 10²² Kg

Numerical Problems (Solved):

Question 1.
Two spheres of 1 kg mass each are separated by 3 m. Calculate the gravitational force between then. Given G = 6.67 × 10^-11 Nm²/kg².
Solution:
Here m₁= m₂ = 1 kg
Distance between two spheres, (r) = 3 m
Gravitational constant (G) = 6.67 × 10^-11 Nm²/kg²
We know
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 10

Question 2.
The radius of moon is 1.7 × 10⁶ m and its mass is 7.35 × 10²² kg. What is the acceleration due to gravity on the surface of moon? Given G = 6.67 × 10^-11 Nm²/kg²
Solution:
Radius of moon, (R) = 1.7 × 10⁶ m
Mass of moon, (M) = 7.35 × 10²² kg
Gravitational constant, (G) = 6.67 × 10^-11 Nm²/kg² (Given)
We know, Acceleration due to gravity on moon
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 11

Question 3.
Find the change in weight percentage of a body when it is taken from equator to poles. Polar radius is 6357km and equitorial radius is 6378km.
Solution:
Polar radius, (r) = 6357 km
Equitorial radius (R) = 6378 km
∴ h = R – r
⇒ h = (6378 – 6357)km
h = 21km
R = 6400 km(Approx)
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 12

Question 4.
At what height above the earth surface, the acceleration due to gravity will be half that on the surface of earth? Suppose R is the radius of earth.
Solution:
Let h be the height above earth surface where
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 13

Question 5.
A ball is dropped from top of 40 m high tower. What will be its velocity after covering a distance of 20 m ? What will be its velocity on striking the earth?
Answer:
1. Here, height of the tower, (h) = 40 m
Initial velocity, (u) = 0
Acceleration due to gravity, (g) = 10m/s²
Distance covered (S) = 20m
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 15
i.e. Velocity of ball when it strikes the earth. = 20 m/s

Question 6.
If weight of an object is 49 N then what will be its mass?
Solution:
Weight of the object W = 49 N
g = 9.8 m s^-2
We know, weight = Mass × acceleration due to gravity
W = m × g
49 = m × 9.8
or m = $\frac {49}{9.8}$
∴ m = 5 kg

Question 7.
Ah object is projected vertically upward with a velocity of 50 m/s. After what time the object will attain the maximum height.
Solution:
Initial velocity of the object (u) = 50 m/s [upward direction]
Acceleration due to gravity, (g) = – 10 ms^-2 [object comes to rest]
Velocity of the object at maximum height,
(υ) = 0
Time taken (t) =?
We know, υ = u + gt
0 = 50 + (-10) × t
0 = 50 – 10t
or 10t = 50
∴ t = $\frac {50}{10}$ = 5s
So the object will attain its maximum height after 5 seconds.

Question 8.
A stone is dropped from the edge of a rooftop. If it crosses 2 m high window in 0.1 second then what is the distance between the upper end of window and the roof?
Solution:
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 16
Distance covered in crossing the window
(S) = 2 m
g = 9.8 ms^-2
t = 0.1 s
Let υ be the velocity of the stone when it reaches the upper edge A of the window.

Question 9.
A helicopter drops food packet for people caught in stationary boat. This is moving at a height of 20 m with a horizontal velocity of 2 m/s. When food packet is dropped the nearest end of the boat is just below the helicopter. If boat is 5 m long shall people caught in the boat receive the dropped food packets?
Solution:
h = 20 m, u = 2 m/s g = 10ms^-2
Vertical Range (R) = $\frac{2 \sqrt{2 h}}{g}$
= $\frac{2 \sqrt{2 \times 20}}{10}$
= 2$ \sqrt{{4}} $
= 2 × 2 = 4 m
But lenght of boat, = 5m
So people caught in the boat will receive food packets.

Question 10.
An object of volume V is immersed in a liquid of density ρ. Calculate the magnitude of buoyant force acting on the object due to the liquid.
Solution:
By Archimedes’ principle, the magnitude of buoyant force,
U.F. = Weight of liquid displaced = Volume × Density × g or
or U.F. = Vρg

Question 11.
The pressure exerted by the weight of a cubical block of side 4 cm on the surface is 10 pascal. Calculate the weight of the block.
Solution:
Here pressure exerted, P = 10 pascal = 10 Nm^-2,
Area, A = 4 cm × 4 cm
= 16 × 10^-4 m²
As P = $\frac {F}{A}$
= $\frac {W}{A}$
W = P × A
= 10 Nm^-2 × 16 × 10^-4m²
= 1.6 × 10^-2 N

Question 12.
The volume of a 500 g sealed packet is 350 cm³. Will the packet float or sink in water if the density of water is 1 g cm^-3? What will be the piass of the water displaced by this packet?
Solution:
Mass of packet = 500 g
Volume of packet = 350 cm³.
Density of packet = $\frac{\text { Mass }}{\text { Volume }}$
= $\frac{500 \mathrm{~g}}{350 \mathrm{~cm}^{3}}$
= 1.43 g cm^-3
Since its density (1.43 g cm^-3) is more than that of water (1 g cm^-3) thus, the sealed packet will sink in water
Volume of water displaced = Volume of packet
= 350 cm³
Mass of water displaced = Volume × Density
= 350 cm³ × 1gcm^-3
= 350 g

Question 13.
A block of wood is kept on the table top. The mass of wooden block is 5 kg and its dimensions are 40 cm × 20 cm × 10 cm. Find the pressure exerted by the wooden block on the table top if it is made to lie on the table top with its sides of dimensions (a) 20 cm × 10 cm and (b) 40 cm × 20 cm.
Solution:
Here, M = 5kg and g = 9.9 ms^-2
Weight = force exerted on table top
= mg
= 5 × 9.8
= 49 N
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 18

Question 14.
A solid body floating in water has $\frac {1}{6}$th of its volume above the surface.
What fraction of its volume will project upwards if it floats in a liquid of density 1,020 km m^-3?
Solution:
Let V be the volume of the body
Volume inside water = V – $\frac {V}{6}$
= (1 – $\frac {1}{6}$)V
= $\frac {5}{6}$V
Upward thrust in water = $\frac {5}{6}$ × 1,000 × g N ……………..(i)
where density of water is 1,000 kg m^-3
Let υ be the volume of the body outside the liquid of density, 1,020 kg m^-3.
∴ Volume inside the liquid = (V – υ)
Upward thrust in liquid = (V – υ) × 1,020 × g N ……….(ii)
Upward thrust in two cases must be the same and must be equal to the weight of the body.
PSEB 9th Class Science Important Questions Chapter 10 Gravitation 19

Very Short Answer Type Questions:

Question 1.
What is g on the moon as compared to that on earth?
Answer:
Nearly $\frac {1}{6}$th of its value on earth.

Question 2.
What is unit of G?
Answer:
It is Nm² kg^-2.

Question 3.
What is the mass of the earth?
Answer:
It is about 6 × 10²⁴ kg.

Question 4.
What is essential property of matter-mass or weight?
Answer:
Mass is the basic and essential property. It is constant everywhere. Weight of a body varies from place to place.

Question 5.
What is SI unit of weight of a body?
Answer:
It is newton (N).

Question 6.
The earth’s gravitational force causes an acceleration of 5 m s^-2 on a 1 kg mass somewhere in the space. How much will be the acceleration of a 3 kg mass at that place?
Answer:
Same i.e., 5ms^-2 since g at a place is independent of mass of the body.

Question 7.
Why one can jump higher on the surface of moon than on the earth?
Answer:
The g at moon surface is nearly 1/6th of that at the surface of earth. Hence one can jump six times higher on the moon with a given initial velocity.

Question 8.
Give the value of universal gravitational constant in S.I. units.
Answer:
(G) = 6.67 × 10^-11 Nm²/kg²
The value of gravitational constant.

Question 9.
The value of ‘G’ on the surface of earth is 6.67 × 10^-11 Nm²/kg². What is its value on the surface of moon?
Answer:
Since G is universal constant so its value on moon surface will be same as on the earth surface i.e. G = 6.67 × 10^-11 Nm²/kg² .

Question 10.
State two factors on which the gravitational force between two objects depends.
Answer:
The gravitational force between two objects depends on: (i) their masses (ii) distance between them.

Question 11.
Write the formula to find the magnitude of gravitational force between the earth and an object on the surface of the earth.
Answer:
F = $\mathrm{G} \frac{\mathrm{Mm}}{r^{2}}$

Question 12.
Can the mass of a body be zero.
Answer:
No, mass of body can never be zero.

Question 13.
Mass of an object on the earth is 600g. What will be its mass on moon?
Answer:
Mass of the object on moon will be same i.e. 600 g.

Question 14.
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Answer:
Mass is a constant quantity. So, it can not be more or less than 42 kg.

Question 15.
How does the value of ‘g’ vary from equator to poles?
Answer:
The value of ‘g’ increases as we move from equator to poles.

Question 16.
What will be the weight of an object on the earth whose mass is 10 kg?
Answer:
Weight of the object on earth
(W) = m x g
= 10 kg × 10 m s^-2
= 100 N

Question 17.
Write the S.I. unit of G.
Answer:
Nm²/kg².

Question 18.
When does an object float when placed on the surface of water?
Answer:
If the density of object is less than water, it will float.

Question 19.
While swimming why do we feel light?
Answer:
The swimmer experiences an upward force by water, this causes buoyancy and makes the swimmer feel light.

Question 20.
Why does a truck or a motor-bus has much wider tyres?
Answer:
So that pressure acting on the road due to weight of truck or motor-bus may be small.

Question 21.
An army tank weighing more than a hundred tonne move conveniently on an earthen road. How?
Answer:
The army tank rests upon a continuous broad chain. So, the total surface area is large and pressure on road due to weight of tank is not very high.

Question 22.
What is the unit of relative density? Why?
Answer:
Relative density has no unit because it is a ratio of two terms having same units. So relative density is expressed in numbers only.

Question 23.
The weight of an object on the moon is ………………. of its weight on the earth.
Answer:
The weight of an object on the moon is 1/6th of its weight on the earth.

PSEB 10th Class Science Notes Chapter 14 Sources of Energy

December 21, 2024December 20, 2024 by Bhagya

This PSEB 10th Class Science Notes Chapter 14 Sources of Energy will help you in revision during exams.

PSEB 10th Class Science Notes Chapter 14 Sources of Energy

→ No activity is possible without energy.

→ Renewable sources of energy are sun, water, and wind, etc.

→ Substances having low ignition temperatures are called inflammable substances.

→ Substances burn at a moderate rate during slow combustion. Substances burn in a very short span of time during rapid combustion.

→ During spontaneous combustion substances suddenly catch fire when their temperature is raised above ignition temperature.

→ Gobar gas is produced by fermentation of cow-dung by anaerobic bacteria.

→ Gobar gas or biogas is a fuel of high calorific value.

→ Solar energy is the combination of visible infrared radiations and invisible (ultra-violet) energy radiated out by the sun.

→ Solar cookers, solar heaters, solar furnaces, and solar cells are devices using solar energy.

→ Solar cells convert solar energy directly into electric energy. Solar cells are used to supply electric energy to watches, calculators, and satellites.

→ Excessive use of any source of energy disturbs the environment. We should try to use non-polluting (clean), economical and efficient sources of energy.

→ Non-polluting sources of energy like solar and wind energy need to be promoted.

→ It is neat and clean energy which is available free of cost.

→ Energy: The capacity of doing work is called energy.

→ Kinetic Energy: It is the energy possessed by a body due to motion, e.g., moving air, running water, etc.

→ Solar Energy: The energy obtained from the sun.

→ Wind Energy: The kinetic energy contained in a large mass of air in motion is called wind energy.

→ Solar Cooker: It is a device that uses solar energy for cooking food.

→ Solar Cell: A device that converts solar energy into electric energy.

→ Ocean Thermal Energy (O.T.E.): There is always the same temperature difference- between water at the surface of the ocean and water at the depth. This difference can be even 20° C. The energy available in this form is called ocean thermal energy.

→ Salinity Ingredients: The variation of concentration of salt is called salinity ingredient.

→ Fuel: Those substances which burn to produce heat energy are called fuels.

→ Biomass: The material present in the bodies of plants and animals is known as biomass.

→ Biogas: It is a mixture of methane (CH₄), Carbon dioxide (CO₂), and Hydrogen Sulphide (H₂S) gas. It is produced by anaerobic fermentation of plants and animals waste (Gobar) and human wastes (feaces) in the presence of water.

→ Destructive Distillation: The process of heating in the absence of air to a high temperature is called destructive distillation. From the destructive distillation of coal-coaltar, coke and coal gas are obtained.

→ Fossil Fuel: Fossil fuel is formed by dead remains of plants and animals under the surface of the earth due to changes in temperature and pressure. Coal, petroleum, and natural gas are fossil fuels.

→ Liquefied Petroleum Gas (L.P.G.): Liquefied Petroleum Gas is a domestic fuel. It is a mixture of ethane, butane, and isobutane gases.

→ Synthetic Petroleum: It is formed by the reaction of coal with hydrogen at high temperatures and pressure.

→ Ignition Temperature: That particular temperature at which a substance starts burning is called ignition temperature.

→ Calorific Value of Fuel: The amount of heat produced by the complete combustion of 1 g mass of a fuel is called the calorific value of the fuel.

→ Slurry: The mixture of gobar (cow dung) and water obtained as a residue in the biogas plant is called slurry.

→ Propellant: Rocket fuel is called propellant. It is a mixture of some concentrated fuel and oxidizing substances.

→ Tidal Energy: That energy that is produced due to the rise and fall of the water level is called tidal energy.

→ Wave Energy: That energy that is produced due to the kinetic energy of waves near the seashore is called wave energy.

→ Geothermal Energy: Due to changes in the interior of the earth, energy produced from the conversion of underground water into steam is called geothermal energy.

→ Nuclear Energy: The energy produced due to nuclear fission reactions of atoms of heavy metals is called nuclear energy.

→ Nuclear Fission: The process of splitting of an atom of the heavy nuclear element by the bombardment of neutrons into light nuclei with the evolution of energy is called nuclear fission.

→ Nuclear Fusion: The process of combining light nuclei to form a heavy nucleus with the release of energy is called nuclear fusion.

→ Greenhouse Effect: The increase of temperature of the atmosphere due to the absorption of ultraviolet rays coming from the sun by carbon dioxide (CO₂) present in the air is called the greenhouse effect.

PSEB 10th Class Science Notes Chapter 13 Magnetic Effects of Electric Current

December 21, 2024December 20, 2024 by Bhagya

This PSEB 10th Class Science Notes Chapter 13 Magnetic Effects of Electric Current will help you in revision during exams.

PSEB 10th Class Science Notes Chapter 13 Magnetic Effects of Electric Current

→ A current-carrying conductor behaves like a magnet. Magnet and electricity are related to each other.

→ Hans Christian Oersted did remarkable work to make us understand electromagnetism.

→ That end of freely suspended magnet which points towards north direction is called North Seeking or the North Pole and the other end which points towards south direction is called South Seeking or the South Pole.

→ Like poles repel each other while unlike poles attract each other.

→ The field or area around a magnet in which its effect or force can be experienced is called the magnetic field of the magnet.

→ The direction of magnetic lines of force inside the magnet is from the south pole to the north pole while outside the magnet it is from the north pole to the south pole. Therefore, magnetic lines are closed curves.

→ Two magnetic lines of force never intersect each other.

→ On passing a current through a metallic conductor, the magnetic field is produced around it.

→ The magnetic field produced all around it is inversely proportional to its distance.

→ The magnetic field at a point inside the magnetic field produced due to the current flowing through a conductor is proportional to the current flowing through the conductor.

→ A coil consisting of a cylindrical-shaped coil having closely packed turns of insulated copper wire is called a solenoid.

→ Inside a solenoid, magnetic lines of force are just like parallel straight lines. The magnetic field is the same at all points inside the solenoid.

→ The force acting in a conductor is in the direction of current and perpendicular to the direction of the magnetic field. This is called Fleming’s left-hand rule.

→ Electric motor, electric generator, loudspeaker, microphone, and electric meter are related with current-carrying conductor and magnetic field.

→ Production of the magnetic fields is necessary for our heart and brain.

→ MRI is important in medical treatment.

→ The electric motor is a device in which electrical energy is transformed into mechanical energy.

→ Electric motors find their use in electric fans, refrigerators, electric mixers, washing machines, computers, MP3 players, etc.

→ In electric motors, a rectangular coil of insulated wire is placed in between two poles.

→ That device that alternately changes the flow of current is called an AC motor.

→ Soft iron core and coil together form an armature. This increases the power of the motor.

→ Faraday discovered how the moving magnet can be used in producing current.

→ A galvanometer is an instrument that is used to detect the presence of current in a circuit.

→ That process by which the change in the magnetic field of a conductor produces a current in another conductor is called electromagnetic induction.

→ When the direction of motion of a coil is perpendicular to the direction of the magnetic field, then the induced electric current in the coil becomes maximum.

→ In electric generators, mechanical energy is used to rotate a conductor placed in a magnetic field as a result of which current is produced.

→ The device used to produce electricity is called an A.C. generator.

→ Electromagnet: A soft iron piece placed inside an insulated conducting coil becomes an electromagnet on passing current.

→ Magnetic Field: The field around a magnet in which its effect can be felt.

→ Solenoid: A coil made by winding a conducting wire having a large number of closed turns.

→ Iron Core: The soft iron rod placed inside the solenoid is called the iron core.

→ Snow Rule: When a wire placed above a magnetic needle carries current from the south direction to the north direction then the north pole (N-pole) of the magnetic needle gets deflected westward.

→ Electromagnetic Induction: Due to change in the magnetic field the current produced in the neighboring coil is called electromagnetic induction.

→ Electric Energy: The capacity for doing work by an electric current is known as electric energy.

→ Electric Power: The rate at which electric energy is consumed in a conductor is called electric power.

→ Electric Generator: The instrument which produces electric current is called an electric generator.

→ Alternating Current (A.C): That current which continuously changes direction alternately is called alternating current.

→ Direct Current (D.C.): That current which has the same direction always is called direct current (D.C.)

→ Short Circuit: When the live wire comes in direct contact with the neutral wire due to damaged wiring or uncovered wire, the resistance of the circuit becomes zero, and the current flowing through the circuit increases suddenly. This is called short-circuiting.

→ Fuse (Safety Fuse): A wire of low melting point connected in an electric circuit is called a fuse.

→ Electric Meter: A device that is connected to an electric circuit to measure electric energy being used is called an electric meter.

→ Electric Shock: When any part of the human body touches any point of the unsheathed (without insulation) circuit having high potential, shock is experienced which is known as electric shock.

→ Overloading: If the current through a circuit is more than the maximum prescribed limit then the wires become hot and may catch fire. It is called overloading.

→ Right Hand Thumb Rule: If we imagine that current is passing through a conductor held in your right hand such that the thumb points in the direction of current then the curling fingers would represent the direction of the magnetic field.

→ Flemming’s Left-Hand Rule: Stretch your left hand in such a way that the first central fingers are mutually perpendicular to each other, then if the first finger points in the direction of the magnetic field, the central finger in the direction of current then the thumb points in the direction of motion of the conductor.

→ Earthing: The joining of metallic frame of the electric appliance of high power with the earth wire of domestic circuit is called earthing.

PSEB 10th Class Science Notes Chapter 12 Electricity

December 21, 2024December 20, 2024 by Bhagya

This PSEB 10th Class Science Notes Chapter 12 Electricity will help you in revision during exams.

PSEB 10th Class Science Notes Chapter 12 Electricity

→ Electric current is the rate of flow of charge Q through the conductor or it is the charge Q flowing per unit time i.e., I = $\frac{Q}{t}$

→ Charge always flows from a body at a higher potential to a body at a lower potential.

→ Electrostatic potential determines the direction of flow of charge from one body to the other when they are brought in contact.

→ Electrostatic potential at a point is defined as the amount of work done is bringing a unit positive test charge from infinity to that point.

→ Conductors have a large number of free electrons whereas insulators have very few free electrons. The motion of free electrons constitutes the electric current.

→ An electric circuit is a closed path through which electrons flow readily.

→ As per convention, the direction of current is taken as opposite to the direction of the flow of electrons.

→ Electric Current: The rate of flow of charge through a conductor is called electric current.
I = $\frac{Q}{t}$

→ Ohm: The resistance of a conductor is said to be 1 ohm if a potential difference of 1 volt is maintained between its ends and it allows 1 ampere of current to flow through it.

→ Voltmeter: It is a device used to measure the potential differences.

→ Conductor: Those substances which allow the current to flow through them are called conductors or good conductors.

→ Insulators: Those substances which do not allow the current to flow through them are called insulators.

→ Ammeter: It is an instrument used to measure electric current.

→ Rheostat: It is a device that is used to increase or decrease the current flowing through the electric circuit.

→ One Volt: If 1 coulomb of charge is allowed to pass through a conductor and in doing so 1 joule of work is done then the potential difference across its ends is 1 volt.

→ Ohm’s Law: The ratio of potential difference across the ends of a conductor and the current flowing through it is always constant, provided the physical state of the conductor such as temperature and pressure remains unchanged.
i.e. V ∝ I or $\frac{V}{I}$ = R

→ Electrical Energy: The capacity of doing work by an electric current is called electrical energy.

→ Electric Power: The rate of consumption of electric energy in a conductor is called electric power.

→ Watt: Watt is an S.I. unit of electric energy in which 1 joule of work is done in 1 sec. Kilowatt. It is the power of an agent which can do 1000 joule of work in 1 second.

→ Kilowatt Hour: It is that electric energy which is consumed in an electric circuit in 1 hour.

→ Coulombs’ Law: Electric force between two charged particles is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.
F = K$\frac{q_{1} q_{2}}{r^{2}}$

→ Joule’s Law of Heating Effect. If T is the electric current that flows through a resistor ‘R’ and as a result of which heat produced is ‘H’. Then heat produced is directly proportional to the square of the current and time ‘t’
H = I² Rt

PSEB 10th Class Science Notes Chapter 11 The Human Eye and The Colourful World

December 21, 2024December 20, 2024 by Bhagya

This PSEB 10th Class Science Notes Chapter 11 The Human Eye and The Colourful World will help you in revision during exams.

PSEB 10th Class Science Notes Chapter 11 The Human Eye and The Colourful World

→ The eye is the most useful natural optical instrument.

→ Distance between near and far points is called accommodation.

→ The least distance of distinct vision for a normal eye is 25 cm.

→ The retina is the most sensitive part of the eye.

→ Rods present on the retina are sensitive to the intensity of light and cones are sensitive to colours of light.

→ The most sensitive part of the retina where the image of the object is formed is called the yellow spot.

→ The focal length of the eye lens can be varied with the help of ciliary muscles.

→ The defects of the eye are myopia, hypermetropia, presbyopia, astigmatism, and colour blindness.

→ Colour blindness cannot be cured while myopia can be corrected by using a diverging (say a concave) lens of suitable focal length.

→ Hypermetropia can be corrected by using a converging (say a convex) lens of suitable focal length. For correcting presbyopia, bifocal lenses are required. Astigmatism is corrected by using a cylindrical lens.

→ Eyes can be donated after death. Even a person using spectacles, contact lens or who have been operated on for cataract or suffering from hypertension can also donate eyes.

→ The cornea of dead persons’ eyes is removed within 6 hours of death and transplanted in blind persons’ eyes.

→ Eye Lens: It is a convex lens made of a fibrous jelly-like substance on the retina of which the real and inverted image of the object is formed.

→ Cornea: It is a transparent membranous bulged out coating in the front part of the eyeball through which light enters the eye, is called the cornea.

→ Iris: The structure just behind the cornea which controls the size of the pupil is called the iris.

→ Myopia: It is the defect of the eye in which the near objects are clearly visible while distant objects are not distinctly visible.

→ Hypermetropia: The defect of the eye in which the distant objects are clearly visible whereas the near objects are not.

→ Retina: It is a delicate membrane having a large number of light-sensitive cells that become active on being illuminated produce electric signals carried to the brain.

→ Near Point: The shortest distance at which if an object is placed is seen clearly without any strain, is called the near point of the eye.

→ Far Point: The farthest point at which an object is placed is seen very clearly.

→ Cataract: The formation of a milky translucent layer on the crystalline lens is called a cataract which results in less visibility and ultimately complete loss of eyesight.

→ Least Distance of Distinct Vision: The minimum distance at which if the object placed can be seen very clearly is called the least distance of distinct vision.

→ Colour Blindness: That defect of the eye in which a person can see clearly but can not distinguish colours is called colour blindness.

→ Persistence of Vision: The sensitiveness of the retina which retains the existence of image for $\frac{1}{216}$th of a second even after when it is actually removed.

→ Presbyopia: With aging, the power of accommodation of eyes decreases, and the person cannot read. This defect is due to the weakening of the ciliary muscles.

→ Bifocal Lens: Defect of the eye in which a person suffers both from myopia and hypermetropia. Such a person needs a bifocal lens consisting convex lens (lower part) to see near objects and a concave lens (upper part) to see far-off objects.

→ Prism: It is a piece of a transparent refracting medium having two triangular and three rectangular surfaces. These surfaces are inclined to each other.

→ The angle of Prism: The angle between two surfaces of the prism is called the angle of prism.

→ Tyndal Effect: If a strong beam of light is passed through a colloidal solution, the path of the beam becomes visible when seen with a microscope placed at a right angle. This effect is called the Tyndal effect.

PSEB 7th Class Maths MCQ Chapter 4 Simple Equations

December 21, 2024December 20, 2024 by Bhagya

Punjab State Board PSEB 7th Class Maths Book Solutions Chapter 4 Simple Equations MCQ Questions with Answers.

PSEB 7th Class Maths Chapter 4 Simple Equations MCQ Questions

Multiple Choice Questions :

Question 1.
Choose simple equation out of the following:
(a) 3x + 11
(b) 2x + 5 < 11
(c) x – 5 = 7x + 6
(d) $\frac{5 x+6}{6}$
Answer:
(c) x – 5 = 7x + 6

Question 2.
A quantity which takes a fixed numerical value is called :
(a) Constant
(b) Variable
(c) Equation
(d) Expression
Answer:
(a) Constant

Question 3.
In equation 5x = 25 the value of x is :
(a) 0
(b) 5
(c) -5
(d) 1
Answer:
(b) 5

Question 4.
In equation $\frac{m}{3}$ = 2 the value of m is :
(a) 1
(b) 0
(c) 6
(d) -6
Answer:
(c) 6

Question 5.
In equation 7x + 5 = 19 the value of n is :
(a) 0
(b) -2
(c) 1
(d) 2
Answer:
(d) 2

Question 6.
In equation 4p – 3 = 13, the value of p is :
(a) 1
(b) 4
(c) 0
(d) -4
Answer:
(b) 4

Question 7.
The equation of the statement, the sum of number x and 4 is 9 is :
(a) x + 4 = 9
(b) x – 4 = 9
(c) x = 4 + 9
(d) x – 9 = 4.
Answer:
(a) x + 4 = 9

Question 8.
The equation of the statement, ‘seven times m plus 7 = gives 77’ is.
(a) 1m × 7 = 77
(b) 7m + 7 = 77
(c) 7m = 77 + 7
(d) m + 7 × 7 = 77
Answer:
(a) 1m × 7 = 77

Fill in the blanks :

Question 1.
A quantity which takes a fixed numerical value is called …………….
Answer:
Constant

Question 2.
The equation for the statement seven time a number is 42 is …………….
Answer:
7x = 42

Question 3.
If x + 4 = 15, then the value of x is …………….
Answer:
x = 11

Question 4.
If 2y – 6 = 4, then y is equal to …………….
Answer:
y = 5

Question 5.
If 8x – 4 = 28, then x is equal to …………….
Answer:
x = 4

Write True or False :

Question 1.
An equation of one variable is called linear equation. (True/False)
Answer:
True

Question 2.
If x – 3 = 1, then value of x is 2. (True/False)
Answer:
False

Question 3.
If 7m + 7 = 77, then value of m is 10. (True/False)
Answer:
True

Question 4.
If 3 subtracted from twice a number is 5, then the number is 4. (True/False)
Answer:
True

Question 5.
If one fourth of a number is 10 then the number is 40. (True/False)
Answer:
False

PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction

December 21, 2024December 20, 2024 by Bhagya

This PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction will help you in revision during exams.

PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction

→ Light is an external physical agent which produces in us the sensation of sight.

→ When light travelling in one medium falls on the surface of another medium, the following three effects are observed:

A part of the incident light is turned back (or reflected) into the first medium.
Another part travels through the second medium along a changed path (i.e the fight is refracted).
The remaining part is absorbed by the second medium.

→ Objects are always placed in front of the mirror to their left, so u (object distance) is always negative.

→ The focal length of the convex mirror is taken as positive (+) and that of the concave mirror as negative (-).

$PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction$

→ Magnification of a concave mirror forming real image is m = $\frac{v}{u}$ and that of convex mirror and also a concave mirror forming virtual image is m = $\frac{-v}{u}$.

→ All distances measured in the direction of the incident light are taken as positive and distances measured in a direction opposite to the incident ray are taken as negative.

→ The phenomenon of bending of a light ray when it travels from one medium to another medium of different optical densities is called the refraction of light.

→ When a ray of light travels from an optically rarer to an optically denser medium, it bends towards normal.

→ When a ray of light travels from an optically denser to an optically rarer medium, it bends away from normal.

→ The higher the refractive index the more is the denser medium.

→ The ratio of the sine of the angle of incidence (Sin i) to the sine of the angle of refraction (Sin r) is constant, called the refractive index of the medium.

→ The Refractive index of a medium is the ratio of the velocity of light in a vacuum to the velocity of light in a medium.

→ The lens is a portion of the transparent and refracting medium.

→ The relation between the object distance (u), the image distance (v) and the focal length (f) of a lens is called lens formula i.e. $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

→ The power of a lens is the reciprocal of its focal length. Its unit is dioptre.

$PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction$

→ Mirror: Any smooth and polished surface is called a mirror.

→ Reflection of Light: When light falls on a mirror or a polished surface then without any change in the medium it returns into the same medium along a particular direction. This phenomenon of change of path of light is called reflection.

→ Incident Ray: A ray of light coming from a source of light falling on any surface is called an incident ray.

→ Reflected Ray: After reflection, a ray of light coming back from point of incidence into the same medium is called a reflected ray.

→ Incident Point: The point on the reflecting surface where incident ray strikes is called incident point.

→ Normal: The perpendicular drawn at the point of incidence is called normal.

→ The angle of Incidence: The angle between the incident ray and the normal is called the angle of incidence.

→ The angle of Reflection: The angle between the reflected ray and the normal is called the angle of reflection.

→ Ray of Light: The straight path of light is called a ray of light.

→ Spherical Mirror: If the mirror is a part of some hollow sphere whose one surface is polished and the other surface is reflecting then such mirror is called a spherical mirror.

$PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction$

→ Concave Mirror: A spherical mirror whose reflecting surface is towards the centre of a hollow sphere of which the mirror is a part, is called a concave mirror.

→ Convex Mirror: A spherical mirror whose reflecting surface is away from the centre of a sphere of which the mirror is a part, is called a convex mirror.

→ Centre of Curvature: Centre of curvature of a spherical mirror is the centre of a sphere of which the mirror is a part.

→ Pole: The midpoint of a spherical mirror is called the pole of the mirror.

→ Principal Axis: An imaginary line joining the pole and centre of curvature of a spherical mirror is called the principal axis.

→ The radius of Curvature: It is the radius of a sphere of which the spherical mirror is a part.

→ Aperture: That part of the mirror from where actually reflection takes place is called the aperture of the mirror.

→ Principal Focus: It is the point on the principal axis where the rays of light coming parallel to the principal axis after reflection actually meet or appear to diverge is called the principal focus of the mirror.

→ Focal Length: The distance between pole and principal focus of spherical mirror is called the focal length of the mirror. It is usually denoted by f.

→ Magnification: The magnification of a spherical mirror is the ratio of the length (size) of the image to the length (size) of the object. It is denoted by ‘m’.

$PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction$

→ Refraction of Light: The change of path of light when it goes from one medium to another medium is called refraction of light.

→ Transparent Medium: Mediums like air, water, and glass through which light can pass easily are called transparent mediums.

→ Lens: A portion of transparent and refracting medium bounded by two surfaces is called the lens.

→ Power of Lens: The capacity of a lens to converge or diverge light rays is called the power of the lens. It is denoted by ‘P’.

→ Centres of Curvature of Lens: The centres of spheres of which the spherical surfaces of the lens are part, are called centres of curvature of the lens.

→ Principal Axis of Lens: The line passing through the centres of curvature of the lens, is called the principal axis of the lens.

→ Optical Centre: A point of the lens through which rays of light go undefeated, is called an optical centre.

→ Principal Focus of Lens: The point on the principal axis of the lens, where rays coming parallel to the principal axis after refraction either actually converge or appear to diverge, is called the principal focus of the lens.

PSEB 10th Class Science Notes Chapter 9 Heredity and Evolution

December 21, 2024December 20, 2024 by Bhagya

This PSEB 10th Class Science Notes Chapter 9 Heredity and Evolution will help you in revision during exams.

PSEB 10th Class Science Notes Chapter 9 Heredity and Evolution

→ Heredity: It is the transmission of genetic characters from parents to the offspring i.e., from one generation to the next.

→ Variation: The differences among the individuals of a species and also in the offsprings of the same parents are referred as a variation.

→ Every organism produce offsprings either through asexual or sexual reproduction. The individuals produced through these reproductive processes are similar but subtly different.

→ In asexual reproduction, although all the offsprings resemble each other and also to their single parent, yet very minor differences (variations) arise in them.

→ For example, if we observe a field of sugarcane we find very few variations among the individual plants.

→ The reproductive processes give rise to new individuals that are similar, but subtly different.

→ The number of successful variations is maximized by the process of sexual reproduction.

→ Inheritance from the previous generation provides both a common basic body design and subtle changes in it, for the next generation.

→ The second generation will have differences that they inherit from the first generation, as well as newly created differences.

→ Some amount of variation is produced even during asexual reproduction.

→ The selection of variants by environmental factors forms the basis for evolutionary processes.

→ A child bears all the basic features of a human being.

→ Both the father and the mother contribute practically equal amounts of genetic material to the child.

→ Mendel was the first one to keep count of individuals exhibiting a particular trait in each generation.

→ Mendel used a number of contrasting visible characters of a garden pea. Cellular DNA is the information source for making proteins in the cell.

→ A section of DNA that provides information for one protein is called the gene for that protein.

→ Plant height can also depend on the amount of a particular plant hormone. Genes control characteristics or traits.

→ Each cell will have two copies of each chromosome, one each from the male and female parents.

→ Every germ cell will take one chromosome from each pair and these may be of either maternal or paternal origin.

→ In some animals, the temperature at which fertilized eggs are kept determines whether the animals developing in the eggs will be male or female.

→ In other animals, such as snails, individuals can change sex, indicating that sex is not genetically determined.

→ Human has 23 pairs of chromosomes.

→ Women are XX, while men are XY.

→ The frequency of inherited traits changes over generations.

→ The germ cells of sexually reproducing populations are made in specialized reproductive tissue.

→ Change in non-reproductive tissues cannot be passed on to the DNA of the germ cells..

→ An individual cannot pass on to its progeny the experiences of its lifetime.

→ Charles Darwin formulated in his hypothesis that evolution took place due to natural selection.

→ We often associate Darwin solely with the theory of evolution.

→ J.B.S. Haldane, a British scientist (who became a citizen of India later), suggested in 1929 that life must have developed from the simple inorganic molecules which were present on earth soon after it was formed.

→ Some basic characteristics will be shared by most organisms.

→ The cell is the basic unit of life in all organisms.

→ Bacterial cells do not have nuclei while the cells of most other organisms do.

→ Among multicellular organisms, whether they can undertake photosynthesis or not, is an important level of classification.

→ The skeleton is inside the body or around the body is another fundamental design difference.

→ The more characteristics two species will have in common, the more closely they are related.

→ The more closely they are related, the more recently they will have had a common ancestor.

→ Non-living material must have given rise to life.

→ The characteristics in different organisms would be similar because they are inherited from a common ancestor.

→ Mammals have four limbs, as do birds, reptiles, and amphibians.

→ The wings of birds and bats are more closely related to each other.

→ The preserved traces of living organisms are called fossils.

→ If we dig into the earth and start finding fossils, it is reasonable to suppose that the fossils we find closer to the surface are more recent than the fossils we find in deeper layers.

→ The dating of fossils is done by detecting the ratios of different isotopes of the same element in the fossil material.

→ The complex organs 4vill be created bit-by-bit over generations.

→ Like the wing, the eye seems to be a very popular adaptation.

→ The structure of the eye in different organisms is different. It shows that they have separate evolutionary origins.

→ A flatworm named Planaria has very simple ‘eyes’ that are really just eye spots that detect light.

→ A change that is useful for one property to start with, can become useful later for quite a different function.

→ Feathers, for example, can start out as providing insulation in cold weather but later, they might become useful for flight.

→ The birds are very closely related to reptiles.

→ Humans have started cultivating wild cabbage as a food plant for over more than two thousand years and generated different vegetables from it by selection.

→ Changes in the DNA during cell division would lead to changes in the proteins that are made from new DNA.

→ The organisms which are more distantly related will accumulate a greater number of differences in their DNA.

→ It is not true that human beings have evolved from chimpanzees. The two resultant species have probably evolved in their own separate ways to give rise to the current forms.

→ Evolution is simply the generation of diversity and the shaping of diversity by environmental selection.

→ The tools for tracing evolutionary relationships are excavating, time-dating, and studying fossils, as well as

→ DNA sequences determination has been used for studying human evolution.

→ All humans are a single species. We all come from Africa.

→ The earliest members of the human species, Homo sapiens, can be traced in Africa.

→ The origin of man, like other species on the earth, is an event of biological evolution.

→ Genetics: The branch of biology which deals with the study of heredity and variation is called genetics.

→ Heredity: The transmission of characters from generation to generation is called heredity.

→ Gene: The basic unit of heredity which transmits the traits into the next generation.

→ Sex chromosome: The pair of chromosomes which decide the sex of male and female.

→ Homologous chromosome: The pair of chromosomes each from mother and father together is called a homologous chromosome.

→ Autosomes: The chromosomes other than sex chromosomes are autosomes.

→ Evolution: The slow and continuous process of changing organisms from simple to complex form is called evolution. In simple words descend with modification.

→ Homologous organs: The organs have the same origin and basic structure but are adapted to perform various functions.

→ Analogous organs: The organs have a different origin and basic structures but perform the same function.

→ Transgenic organism: The organism produced by the introduction of foreign DNA or genes.

→ Fossils: The remains of dead animals in earth strata are called fossils.

→ Haploid: The single set of chromosomes obtained from one parent.

→ Nucleotide: A molecule made up of nitrogen base, sugar, and phosphate.

→ Chromatid: When the chromosomes divide into two each part is called a chromatid.

→ Vestigial organs: Organs in our body having no functional importance are called vestigial organs.

→ Genetic drift: The effect on the genetic continuation in a population due to the death of organisms or immigration is called genetic drift.

→ Variations are differences between young one of the same parent: They differ from their parents.

→ Variations arise due to inaccuracies in DNA replication in asexually reproducing organisms.

→ Offsprings: Young ones produced as reproduction are ailed offsprings.

→ Genotype: The internal genetic constitution of an organism is termed genotype. The environment has no effect on it.

→ Phenotype: It refers to externally visible characters of an organism. It is the net result of interactions between genotype and environment. Individuals of the same genotype breed alike are termed phenotype.

→ Recessive traits: An allele (gene) that is not expressed phenotypically when present in heterozygous conditions.

→ Speciation: The origin of species is termed speciation.

→ Acquired characters: The characters acquired during a lifetime are ailed acquired characters.

→ Life: Life is the power that an organism possesses to maintain and reproduce itself.

→ Natural selection: According to Darwin the individual with special traits survive and multiply while others perish is called natural selection.

PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I

December 20, 2024December 19, 2024 by Bhagya

This PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I will help you in revision during exams.

PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I

Introduction:
Word processing is the most commonly used software in computers, with the help of this, we can create documents, save the documents, print the documents and also we can edit the already created document. Let’s learn about these features of word processing.

Wort Processing:
We make a lot of mistakes when typing a document with the help of typewriter, which we can’t correct again, we have to type the document again to make it better, but word processing gives us a facility through which we can easily correct our mistakes in typed documents without having to retype them.
Word processing is a process by which we can create, save and print any type of document in a computer and it can be used anytime in the future and can be edited if required.
The software that is used for word processing process called word processor. For example: MS Word, NotePad, WordPad and word perfect all are word processors.

Features of Word Processing:
Following are the features of word processor:

A word processor provides an easier and faster method to type the text.
It offers so many styles, size, color, effects for text.
Using a word processor, you can apply editing operations to the text.
It stores all your documents for. future use.
It allows you to insert photos, music, background etc. into the document.
It can move any document from one place to another with the help of cut, copy, and paste option.
You can delete, edit, update the data in the pre-created document at any time.
It helps us to find and correct mistakes in the typed text.
It also provide the facility to check the grammar mistakes in the typed text.

Word Processing – Software:
A word processor is a software program capable of creating, saving and printing typed documents. Today, the word processor is one of the most widely used software programs on the computer, it can create different types of files and to create these files requires different software such as WordPad, Microsoft Office, Microsoft Word, etc are some examples of word processors.

Today in this lesson we will read about MS Word word processor.

Microsoft Word
Microsoft Word is a word processor software program published by Microsoft Company also called MS Word, WinWord, Word. Microsoft Word provides advanced features for creating and saving different types of documents. For example, we can create letter typing, emails, reports, tables, etc. in Microsoft Word.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 1

Some of the basic applications of MS Word are as follows:

Creating and saving a text document.
Editing and formatting existing documents.
Make the document attractive with the help of different styles, size, colors and effects.
Creating graphical documents with images, charts, smart art etc.
Identify grammatical and spelling errors in the document.

Features of Microsoft Word
Some of the special features of Microsoft word are as follows:

MS Word allows us to include text anywhere in the document.
We can delete any word, line or page from the document as easily as we erase the words written on paper.
We can cut and copy the text and paste it anywhere in the same document or any other document.
MS Word allows us to set the page margin and page size according to our needs.
We can add Bold, Italic and Underline effects to the text.
We can change the size, style, color of the text.
We can add header on the top of pages and footer on the bottom of the page.
We can add pictures, chart, graphs and smart art.
We can convert the text into tables.
You can also set different margins in a document and also determine the different locations to start a paragraph.
It also provides us with the facility of macro. This is a list of many commands with which our time is saved.
MS Word also provides us the facility of spelling checks. It shows a red line below the words that are incorrect.
MS Word also provides us the facility of grammar checks.
It also provides Find and Replace option.
It also provides the facility of dictionary with which we can find many words with the same meaning and use them in our document.

Starting MS Word
The steps to start MS Word are as follows:
1. First, click the Start button
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 2
on the desktop

2. Now click on All Program from the popup menu as shown in the picture below.

3. Now click MS Office! MS Word.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 3
Or
Type “Word” in the search bar as shown in the picture below and press Enter key from the keyboard

Components of MS Word Window
When you start the Word application then a window opens on the screen as shown in the picture below. Let us understand the different important parts of this window.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 5
1. File Menu: This option is available in the upper left corner of the window, it contains many of the following commands:
(a) Home: It has options like font color, font size, font style, alignment, bullets, line spacing, etc. All the basic elements that someone might need to edit their document are available in the Home option.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 6
(b) Insert: Tables, sizes, images, charts, graphs, headers, footers, page numbers, etc. are available in insert options.

(c) Design: The template (pre-created document design) or the design in which you want your document to be created can be selected under the Design tab.

(d) Page layout: Under the Page Layout tab we can find the options such as Margins, Orientation, Columns, Lines, Indentations, Spacing, etc.

(e) Reference: This tab is most useful for those who are preparing thesis or writing books or working on a long document. Footnote, table of content, bibliography, captions etc. options can be found under this tab.

(f) Review: Spell check, grammar, thesaurus, word count, language, translation, comments, etc. can all be tracked under the Review tab.

2. Quick Access Toolbar: Collection of buttons that provide one click access to commonly used commands such as Save, Undo or Redo. You can also customize this according to your preference.

3. Title Bar: This bar window is at the top of the screen and the name of the open document appears on it. Above this bar are three control buttons:

minimize, maximize, close button

4. Ribbon: The ribbon consists of three organized commands:
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 8
(a) Tabs: These appear on the top of the ribbon and contain groups of related commands. For example: home, insert, page layout ribbon, references, mailings Review etc. all are tabs. We have already read about them.
(b) Group: They handle related commands; the name of each group appears below the group on the ribbon. For example, a group of commands related to fonts (Font Group) or a group of commands related to alignment (paragraph group), etc.
(c) Commands: Commands appear in each group as described above. For example: Cut, Copy, Paste, Font Size, Color, Alignment etc. are all commands.

5. Ruler: There are two rulers in the word window – a horizontal ruler and a vertical ruler. The horizontal ruler appears just below the ribbon and is used to set margins and tab stops. The vertical ruler appears on the left side of the word window and is used to determine the vertical position of the page.

6. Help: The help icon can be used whenever you want to get help related to MS Word. It provides excellent tutorials on various topics related to Word.

7. Document Area: Right below the ruler, there is a large space called the text area. This is the area where we type our document; the blinking line in this area is called the insertion point which indicates that your typing will start from this place.

8. Status Bar: It displays the information of the document as well as the position of the insertion point. From left to right, this bar contains information on the total number of pages and words, document language, etc.

9. Dialog Box Launcher: This appears as a very small arrow in the lower-right corner of most groups of the ribbon. Clicking this button opens a dialog box or task pane that provides more options about the group.

10. View buttons: At the bottom right of the window screen is a set of 5 buttons that allow us to view the document in a different view.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 9
(a) Prints Layout: This is the default document view in Word. The Print Layout view shows the document as it would appear after printing.
(b) Full-Screen Layout View: This view opens the document to a full screen. This layout helps us to make our document easily readable above the screen.
(c) Web Layout: This view displays a document on the screen the way it will look when viewed in a Web browser if you saved it as a web page.
(d) Out Line View: The outline view shows the document as an outline form.
(e) Draft View: This is the most commonly used view, in this view we can edit our document very quickly and easily.

Creating a New Document
Follow these steps to create a new document:
PSEB 7th Class Computer Notes Chapter 2 Windows Explorer 1

Click the office button and then click File menu
Now click on New option from the drop down menu, as shown in the picture.
A New Document dialog box will appears on the screen.
Click Blank Document option from this dialog box and then Click Create Option as shown in picture.
Now a blank document will appear on the screen

Or
You can create a new document by pressing the Ctrl + N keys from the keyboard.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 11
Open an Existing Document
Follow these steps to open an existing document:

Click the File tab or Office Button.
Click Open option. The Open dialog box appears.
As shown in picture below select a document which you want to open and then Click Open button.
Now your document will open on the screen.

Or
You can open an existing document by pressing the Ctrl + 0 keys from the keyboard.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 12

Saving a Document
To save a newly created document follows these steps:

Click the File tab or Office Button.
Click Save option. The Save dialog box appears. As shown in picture below.
Now type the name of your document in File name box and then click Save button.

Or
You can also save your document by pressing the Ctrl + S keys from Keyboard Now your document is safe for future use.
PSEB 7th Class Computer Notes Chapter 3 Microsoft Word Part-I 13

Note:

Word processing is a process by which we can create, save and print any type of document
The software that is used for word processing process called word processor.
MS Word, NotePad, WordPad and word perfect are all word processors.
Microsoft Word is a word processor software program, provides advanced features for creating and saving different types of documents.
Tabs appear on the top of the ribbon and contain groups of related commands.
Group handle related commands; the name of each group appears below the group on the ribbon.
The large area at the bottom of the ruler is called the text area. We can type our document in this text area.
Text can be viewed on a computer screen before it is printed, errors can be detected and corrected.
A dialog box launcher is present in the lower right corner of each group.
Word allows us to view the document in 5 different views. Prints Layout. Full screen layout view, Web Layout, Out Line View, Draft view.