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This PSEB 8th Class Science Notes Chapter 16 Light will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 16 Light

→ Light is a form of energy.

→ Light travels in a straight line.

→ Light enables us to see the objects around us.

→ Light reflected from the objects falls into our eyes and thus, we can see the objects.

→ Those objects, which emit their own light, are called luminous objects.

→ The objects, which do not emit light of their own, but reflect light falling on them, are called non-luminous objects.

→ Polished or shiny surfaces reflect light.

→ A mirror changes the direction of light, that falls on it.

→ The angle of incidence (∠i) is always equal to the angle of reflection (∠r).

→ The incident ray, normal at the point of incidence, and reflected ray all lie in the same plane.

→ A number of reflections can be achieved with the mirrors arranged at an angle.

→ When the light passes through a prism, it undergoes dispersion and white light splits up into seven colours.

→ The spectrum of sunlight consists of seven colours – Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

→ These seven colours can be remembered by the term VIBGYOR.

→ Rainbow is a natural phenomenon of dispersion.

→ The human eye is a sensitive organ, which enables us to see the objects around us.

→ A human eye has a convex lens, whose focal length is adjusted by ciliary muscles.

→ Reflections can be parallel or regular and diffused.

→ Cones and rods are two types of nerve endings found in the blind spots of the eye.

→ Two types of resources for visually challenged persons are Non-optical aids and optical aids.

→ The Braille system is one of the most important and popular resources for visually challenged persons.

→ Reflection of Light: The change in direction of light by a shiny surface is called the reflection of light.

→ Screen: The white sheet or surface on which, the image is obtained.

→ Regular Reflection: Reflection takes place from a polished and regular surface.

→ Scattering of Light: Diffusing of light in all directions.

→ Diffused Reflection: The light rays reflected from the non-polished or irregular surface.

→ Incident Ray: A ray of light from a source of light falling on a given surface.

→ Kaleidoscope: An instrument based on multiple reflections used to create new designs.

→ Mirror: A smooth and shiny surface.

→ Normal: The perpendicular to the polished surface (mirror) at the point of incidence.

→ Source of Light: An object which emits light.

→ Real Image: The image formed, when incident rays after reflection actually meet at a point.

→ Virtual Image: The image formed, when incident rays after reflection do not actually meet but appear to meet at a point.

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

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

→ Power of Accommodation is the ability of the eye to focus the distant objects as well as the nearby objects, at the retina by changing the focal length or converging power of its lens.

→ The least Distance of Distinct Vision is the minimum distance at which an object must be placed so that a normal eye may see the object clearly without any strain on the eye. It is about 25 cm for the normal eye.

→ Myopia or Short-Sightedness means a person can see only nearby objects clearly, but cannot see distant objects. This defect is removed by using spectacles with a concave lens.

→ Hypermetropia or Long-sightedness: A person suffering from this defect can see distant objects clearly but cannot see nearby objects. The defect is removed by using spectacles fitted with a convex lens.

→ Persistence of Vision: Impression of an image on the retina lasts for 0.1 sec after the removal of the object. This effect is known as the persistence of vision.

→ Dispersion of Light is the splitting of white or some other light into its constituents.

→ Perception of Colour:

• The human eye contains a large number of cell rods and cones which are sensitive to light.
• Rods respond to the intensity of light and cones respond to the color of the light.
• If cone cells are absent in the eye, then such a person is colour blind.

This PSEB 8th Class Science Notes Chapter 15 Some Natural Phenomena will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 15 Some Natural Phenomena

→ Sparks, in the sky, was believed to be the wrath of God.

→ In 1752, Benjamin Franklin established that lightning and the spark of amber were the same things.

→ Electricity is responsible for sparks or lightning in the sky.

→ Rubbing produces electric charges in some materials.

→ Similar materials acquire the same charges when rubbed with the same materials.

→ Like charges repel each other.

→ Different materials acquire different charges when rubbed with the same materials or different materials.

→ Unlike charges attract each other.

→ Two kinds of changes are positive and negative.

→ The electric charge generated by rubbing is called static electricity.

→ Static charges are stationary i.e. they do not move.

→ Moving charge constitutes an electric current.

→ Earthing is the process of transfer of charges from a charged object to the earth. Lightning is nothing but an electric discharge.

→ Electric discharge occurs when

• two clouds come together
• clouds come near the earth surface
• clouds and the human body come closer

→ Clouds carry -ve charges on them and on coming in contact with +ve charge produce a huge amount of energy in form of bright light and sound.

→ A house or a building and even a closed vehicle is the safest place during a thunderstorm.

→ A lightning conductor is a device to secure tall buildings from the effect of lightning.

→ Electric cell emits electric discharge, which can be up to 650 volts.

→ Thunderstorms, cyclones, lightning are natural phenomena that cause large-scale destruction of human life and property.

→ Earthquake is also a natural phenomenon.

→ Predictions about thunderstorms, cyclones, and lightning can be done, but earthquakes can not be predicted.

→ An earthquake is the sudden shaking or trembling of the earth.

→ Floods, Landslides, Tsunami are caused by earthquakes.

→ A seismograph is an instrument meant to record seismic waves produced on the surface of the earth by tremors.

→ The intensity of an earthquake is measured in terms of magnitudes on a scale called the Richter Scale.

→ Symmetrical and mud/timber buildings are to be constructed in seismic-prone areas.

→ Static Electricity: The electrical charge excited by rubbing is said to be static electricity.

→ Earthing: The process of transfer of charges from a charged body to the earth is called earthing.

→ Electric Discharge: The process of producing light and sound by clouds is called electric discharge.

→ Thunderstorm: A loud noise produced across the sky during a rainy day is called a thunderstorm.

→ Lightning: A bright light produced across the sky, due to the rubbing of two clouds or clouds and earth, is lightning.

→ Earthquake: The disturbance deep inside the earth’s crust that causes trembling and shaking of the earth, is called an earthquake.

→ Lightning Rod: It is a device to secure tall buildings from the effect of lightning.

This PSEB 8th Class Science Notes Chapter 14 Chemical Effects of Electric Current will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 14 Chemical Effects of Electric Current

→ Some materials that allow current to pass through them are called conductors and some that do not allow the current to pass through them are called insulators.

→ Some liquids that allow an electric current to pass through them, are called electrolytes.

→ An electric bulb glows, when an electric current passes through it.

→ LEDs are used, when the electric current is very small.

→ Pure air is an insulator.

→ Tap water, saltwater, sea or pond water all conduct electricity as they contain impurities and salt them.

→ Pure distilled water is a non-electrolyte.

→ Solutions of acids, bases, and salts are good electrolytes.

→ The passage of an electric current through a conducting solution causes chemical reactions.

→ Evolution of gas, change of color of the solution, and deposits of metal on electrodes are a few examples of chemical effects of electric current.

→ Fruits and vegetables can also conduct electricity.

→ Passing an electric current through acidulated water produces bubbles of oxygen and hydrogen on +ve and -ve terminals respectively.

→ Electroplating is an important application of the chemical effect of electric current.

→ Electroplating is the process of depositing a layer of any desired (superior) metal on another metallic object (of base metal) by means of electricity.

→ Electroplating is very useful to obtain shiny and rust-proof articles by covering cheap metals with desired coatings of costlier metals.

→ Conductors: Materials that allow current to pass through them, are called conductors.

→ Insulators: Materials that do not allow current to pass through them, are called insulators.

→ Electrolysis: It is the process by which a substance (electrolyte) is decomposed into its basic components by passing an electric current through it.

→ Anode: The electrode, which is connected to the positive end of the battery is called the anode.

→ Cathode: The electrode, which is connected to the negative end of the battery is called the cathode.

→ Electrolyte: A salt solution that conducts electricity through it.

This PSEB 8th Class Science Notes Chapter 13 Sound will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 13 Sound

→ Sound is produced by a vibrating object.

→ The maximum distance to which a vibrating body moves on either side from its mean position is called the amplitude of vibration.

→ The time taken to complete one oscillation is called the time period.

→ The number of oscillations per second is called the frequency of oscillation.

→ Frequency is measured in hertz (Hz).

→ The larger the amplitude of vibration, the louder is the sound produced.

→ The higher the frequency of vibration, the higher is the pitch.

→ For human ears, the audible range of frequency is 20 Hz to 20000 Hz.

→ Sound needs a medium for its propagation. It cannot travel in a vacuum.

→ Light travels much faster than sound.

→ The sound may get reflected by an obstacle. The echo is produced due to reflected sound.

→ Some surfaces reflect sound better than others.

→ The pleasant effect of sound on the ear is called music while the unpleasant sound is called noise.

→ In human beings, voice is produced by the vibration of their vocal cords.

→ Amplitude: The maximum distance through which a vibrating body is displaced from its mean position.

→ Echo: The reflection of sound from an obstacle such as a building or a mountain.

→ Frequency: The number of vibrations made by a vibrating body in 1 second.

→ Hertz (Hz): The unit of frequency.

→ Larynx: Organ of voice in human beings.

→ Loudness: The property of sound which depends upon the amplitude and intensity of the vibrating body.

→ Musical Sound: Sound which produces a pleasing effect on the ear.

→ Noise: Sound which produces a disagreeable effect on the ear.

→ Ultrasonic: Vibrations having a frequency above 20,000 Hz.

→ Vibrating Body: An object, moving to and fro about the mean position.

→ Vibrations: To and fro motion of an object.

→ Vocal Cords: Two pairs of membranous cords or folds in the larynx.

This PSEB 8th Class Science Notes Chapter 12 Friction will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 12 Friction

→ Force opposing the motion of the body is called the force of friction.

→ Force of friction acts between any two surfaces in contact with each other.

→ Friction depends upon the nature and smoothness of the surface.

→ Friction is due to irregularities on the two surfaces in contact.

→ Friction increases with pressure.

→ Sliding friction is less than static friction.

→ Friction is both a friend and a foe.

→ Friction is a necessary evil.

→ Friction can be increased or decreased as per requirement.

→ Wheels reduce friction.

→ Lubricants are substances that can reduce friction.

→ The frictional force exerted by fluids is also known as drag.

→ Frictional force in fluids depends upon the speed, nature of the object, and shape of the object.

→ Streamlined objects offer less friction in fluids.

→ Friction: A force which opposes the relative motion between the two surfaces in contact is called friction.

→ Static Friction: A force that counterbalances the applied force on a body is static friction.

→ Sliding Friction: A force that exists between any two sliding surfaces is sliding friction.

→ Rolling Friction: A friction that comes into play between two rolling materials is called rolling friction.

→ Fluid Friction: A force exerted by the fluid on the object immersed in it, is called fluid friction.

→ Streamline: A particular shape that offers little resistance in air or water.

→ Fluids: The name given to air and liquids together.

This PSEB 8th Class Science Notes Chapter 11 Force and Pressure will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 11 Force and Pressure

→ Force is a push or a pull that produces or tends to produce a change in the state of a body.

→ The effect of force depends not only on the magnitude of force but also depends on the area on which it is applied.

→ Force can change the speed, the direction of motion, and the shape of an object,

→ There are various types of forces such as muscular, magnetic, electrostatic, gravitational, and frictional.

→ Force acting per unit area is called pressure.

→ Liquids and gases apply pressure on the surfaces of the container.

→ The atmosphere also exerts pressure, called atmospheric pressure.

→ The pressure exerted by liquids at a given depth is equal in all directions.

→ The pressure of a column of liquid depends on its depth. The more the depth of the liquid column, the more is the pressure.

→ Gases exert pressure in all directions.

→ Force: It is defined as an external cause that changes or tends to change the state of rest or of uniform motion of an object. It is a vector quantity.

→ Resultant Force: When two or more forces act on a body simultaneously, then a single force that produces the same effect as the combined effect of all the forces together, is called resultant force.

→ The force of Friction: The force which opposes the motion of one body over another body in contact with it, is called the force of friction or simply friction.

→ Gravitation: Gravitation is the attraction between any two bodies (particles) in the universe.

→ Weight: The weight of a body is the force with which the body is attracted towards the centre of the earth.

→ Pressure: Force acting per unit area is called pressure.

→ Atmospheric Pressure: Pressure exerted by the atmosphere on all the objects lying on the earth is called atmospheric pressure.

This PSEB 8th Class Science Notes Chapter 10 Reaching the Age of Adolescence will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 10 Reaching the Age of Adolescence

→ It is after growing up to a certain age that human beings and other animals become capable of reproduction.

→ On crossing the age of 10 or 11 in human beings there is a sudden spurt in growth.

→ Growth is a natural process.

→ The period of life when the body undergoes changes, leading to reproduction maturity is called adolescence.

→ Adolescence begins at the age of 11 and lasts upto 18 or 19 years of age.

→ Adolescents are also called teenagers.

→ The human body undergoes severe changes during adolescence which marks the onset of puberty.

→ The most conspicuous change during puberty is height.

→ The rate of growth in height varies in different individuals.

→ All the body parts do not grow at the same rate.

→ Height also depends on the genes inherited from parents.

→ At puberty, the voice box begins to grow. Generally, girls have a high-pitched voice, whereas the voice in boys is deep.

→ During puberty, the secretion of sweat glands and sebaceous glands also increases.

→ Endocrine glands release hormones directly into the bloodstream.

→ Adolescence is also a period of change in a person’s way of thinking.

→ The appearance of secondary sexual characters helps in distinguishing males from females.

→ Changes occurring in adolescence are controlled by hormones which are the chemical substances secreted by endocrine glands.

→ Hormones are secreted by endocrine or ductless glands.

→ The endocrine glands are the pituitary, adrenal, thyroid, and gonads.

→ The pancreas is an exocrine as well as an endocrine gland.

→ Pheromones are the hormones present in insects.

→ An endocrine gland does not have a duct and is, therefore, also called a ductless gland.

→ A ductless or endocrine gland pours its secretion into the circulatory system of the body for sending to the target cells.

→ Secretions of endocrine glands are called hormones.

→ Testes or male gonads are mixed organs that produce sperms as well as male sex hormones or androgens (e.g., testosterone, androsterone).

→ Ovary secretes estrogen and progesterone hormones.

→ The cyclic changes that occur every 28 days (lunar month) in the reproductive tract of human females from the period of puberty to the age of menopause are called the menstrual cycle.

→ At the age of 45-50 women stop menstruation. It is called menopause.

→ There are 23 pairs of chromosomes in humans.

→ There are 22 pairs of autosomes and 1 pair of sex chromosomes in human beings.

→ The change from larva to adult is called metamorphosis. These changes are also controlled by hormones.

→ The physical and mental well-being of an individual is regarded as an individual’s health.

→ Diet for an adolescent has to be carefully planned as it is a stage of rapid growth and development.

→ Personal hygiene is more necessary for teenagers because the increased activity of sweat glands makes the body smelly.

→ All adolescents should take walks, do exercise and play other games.

→ Adolescence: Children between the ages of 10 or 11 years to 18 or 19 years are called adolescents. This period of the age is called adolescence.

→ Puberty: It is a period (11 to 18 years) when the reproductive organs start functioning.

→ Voice Box: It is a box consisting of cartilages present in the throat of human beings causing voice.

→ Adam’s Apple: In boys, the growing voice box is seen as a protruding part of the throat called Adam’s apple.

→ Secondary Sexual Characters: In boys and girls some characters are present which helps to distinguish them. These are called secondary sexual characters.

→ Endocrine Glands: The ductless glands present in animals which secrete hormones and pour them directly into the bloodstream are called endocrine glands.

→ Hormones: These are the chemical secretions secreted by endocrine glands to control the activities of the human body.

→ Target Site: It is a particular body part where hormones released by the endocrine glands through the bloodstream reach.

→ Pituitary Gland: It is a master gland present in the brain.

→ Testosterone: It is a male hormone secreted by the testes at the onset of puberty.

→ Estrogen: It is a female hormone released by the ovaries at the onset of puberty which makes the breasts develop.

→ Sex Chromosomes: Human beings have 23 pairs of chromosomes. One pair out of them (23rd pair) is called a sex chromosome.

→ Thyroxine: It is a hormone secreted by the thyroid gland situated in the neck.

→ Insulin: It is a hormone secreted by the pancreas which controls sugar levels in the blood.

→ Adrenalin: It is a hormone secreted by the adrenal gland which maintains the salt balance in the blood.

→ Balanced Diet: A diet that contains the various components of food (carbohydrates, fats, proteins, minerals, vitamins, water) in the right proportion.

→ Health: The physical and mental well-being of an individual is regarded as an individual’s health.

This PSEB 8th Class Science Notes Chapter 9 Reproduction in Animals will help you in revision during exams.

PSEB 8th Class Science Notes Chapter 9 Reproduction in Animals

→ Reproduction ensures the continuation of similar kinds of individuals, generation after generation.

→ All living organisms reproduce to create more of their own kind. This process is called reproduction.

→ There are two main methods of reproduction.

• Asexual reproduction
• Sexual reproduction

→ In asexual reproduction, a new individual is formed from a single parent.

→ Living organisms reproduce asexually by the following five methods:

• Binary fission
• Budding
• Spore formation.
• Vegetative reproduction
• Regeneration

→ In sexual reproduction, two parents are needed to produce new individuals.

→ The male parent produces male gametes and the female parent produces female gametes.

→ The union of male and female gametes is known as fertilization.

→ There are some organisms in which both the gametes exist in the same individual. Such organisms are called hermaphrodites.

→ The fertilization in some animals is internal and in others external.

→ The process of forming specific shapes and patterns and increasing in size is called development and growth.

→ The growth of parts involves changes in shape, size, and number of constituents.

→ In plants the growth is indefinite but in animals it is definite.

→ The process of formation of the individual from seed, zygote, or body part is called development.

→ There are different ways for the development of individuals.

→ Sexual reproduction is highly evolved.

→ Male Reproductive System consists of a pair of testes, two epididymis, two vasa differentia, accessory glands, two ejaculatory ducts, urethra, and a copulatory organ or penis. Except for testes, all others are secondary male sex organs.

→ The female Reproductive System is made up of a pair of ovaries, a pair of oviducts, uterus, vagina, external genitalia, accessory genital glands, and mammary glands. Except for the first, all others are secondary female sex organs.

→ Semen is a milky fluid produced by the male reproductive system and ejaculated during orgasm.

→ It contains spermatozoa and secretions of glands (seminal vesicles, prostate gland, and Cowper’s glands).

→ The penis is the male copulatory organ that also takes part in the conduction of urine from the body.

→ Spermatazoan (Sperm) is a motile, microscopic male gamete.

→ A typical spermatozoan consists of 4 parts – head, neck, middle piece, and tail.

→ Cloning is the production of an identical cell, carries another living part of a complete organism.

→ The cloned animals are found to be born with severe abnormalities.

→ Sexual Reproduction: A kind of reproduction in which the union of two opposite sexes (male and female) accomplishes fertilization is called sexual reproduction.

→ Asexual Reproduction: A kind of reproduction in which new ones are produced from a single parent is called asexual reproduction.

→ Egg: It is a female gamete produced by the ovary of a female.

→ Sperms: These are male gametes that are produced by the testes of males.

→ Fertilization: The union of male gamete (sperm) and female gamete (egg or ovum) is called fertilization.

→ Zygote: A single-celled structure formed by the union of sperm and egg is called a zygote.

→ Internal Fertilization: Fertilization that takes place inside the body of a female body is known as internal fertilization.

→ External Fertilization: Fertilization that takes place outside the body of females is called external fertilization.

→ Embryo: The zygote divides repeatedly into a structure called an embryo.

→ Foetus: The stage of development of an embryo in which all the body parts are identifiable is called foetus.

→ Viviparous Animals: The animals which produce young ones are known as viviparous animals.

→ Oviparous Animals: The egg-laying animals are known as oviparous animals.

→ Metamorphosis: The drastic change which transforms a larva into an adult is called metamorphosis.

→ Budding: The kind of asexual reproduction in which a new individual develops from the buds is called budding.

→ Binary Fission: A kind of asexual reproduction in which two individuals are produced simply by dividing itself is called binary fission.

→ Cloning: Cloning is the production of an exact copy of a cell or a complete organism.