This PSEB 7th Class Science Notes Chapter 15 Light will help you in revision during exams.
PSEB 7th Class Science Notes Chapter 15 Light
→ A ray coming from a source of light falls on the object and after reflection enters our eyes so that we see the objects.
→ Light always travels in a straight line.
→ The reflection from the surface of the object must be the same to see the image.
→ After hitting a surface, the light returns to the same medium in a certain direction. The process of coming back of the light is called reflection of light.
→ The ray of light that strikes an object is called an incidental ray and the ray of light which after hitting an object returns to the same medium in a particular direction it is called a reflected ray.
→ The angle between the incident ray and the perpendicular drawn at the point of incidence is called the Angle of Incidence.
→ The angle between the reflected ray and the perpendicular drawn at the point of reflection is called the angle of reflection.
→ The angle of incidence and the angle of reflection are always equal. This is called the law of reflection.
→ The image formed on the screen is called a Real image.
→ The image that cannot be obtained on the screen even if the reflected rays appear to meet is called a Virtual image.
→ The image formed by a plane mirror is always formed behind the mirror. This image is virtual is erect and of the same size as that of the object.
→ The image formed by a plane mirror is at the same distance behind the mirror as the object is placed in front of the mirror.
→ The image formed by a plane mirror is laterally inverted i.e. the left side of the object becomes to the right of the image and the right side of the object is seen to be left of the image.
→ A concave mirror is a spherical mirror with a reflecting surface facing inwards.
→ A convex mirror is a spherical mirror with a reflecting surface facing outwards.
→ The rays of light coming from a distant object are considered to be parallel to each other and the point at which they actually meet after being reflected from the mirror or appear to meet is called the focal point of the mirror.
→ For a concave mirror, a virtual, erect, and large image is formed only when the object is placed between the principal focus and the mirror.
→ For a convex mirror, the image formed is erect, virtual, and smaller in size than the size of the object.
→ The lens is a piece of transparent medium surrounded by two surfaces. The two main types of lenses are
- Convex lens
- Concave lens
→ The convex lens is thicker in the middle and thinner at the edges.
→ The concave lens is thin in the middle than at the edges.
→ A convex lens is also called a Convergent lens whereas a Concave lens is called a Divergent lens.
→ The convex lens can be used to see small objects. Hence it is also called magnifying glass or reading glass.
→ On allowing white light to pass through a prism, it splits up into seven colours, which means white light is composed of seven colours.
→ The point at which the rays of light coming from a distant object (such as the sun) meet or appear to meet after suffering refraction from the lens is called the focal point of the lens.
→ When a ray of light enters from one medium to another transparent medium, it changes its path. The phenomenon of light changing its path is called the refraction of light.
→ Reflection of light: When light travelling in a straight line strikes the surface of a mirror or a polished opaque surface, it changes its direction and returns to the same medium. The process of coming back from the light is called the reflection of light.
→ Incidental ray: A ray of light falling on the smooth and polished surface is called an incident ray.
→ Reflected Ray: A ray of light after striking a mirror changes its direction and returns to the same medium, which is called a reflected ray.
→ The angle of incidence: The angle between the incident ray and the perpendicular drawn at the point of incidence is called the angle of incidence.
→ The angle of reflection: The angle formed between the reflected ray and the perpendicular drew at the point of incidence is called the angle of reflection.
→ Point of incidence: The point at which the incident ray strikes the surface of the mirror, is called the point of incidence.
→ Perpendicular: The normal or perpendicular line drawn from point of incidence.
→ Real Image: When the light coming from an object after reflection meets at a point forming an image then such image is called a real image.
→ Virtual reflection: When the rays of light only appear to meet at a point after reflection from a mirror then that point is called a virtual image. A virtual image cannot be obtained on the screen.
→ Spherical Mirror: A mirror whose reflecting surface is a part of a hollow spherical surface.
→ Concave mirror: If the inner surface of a spherical mirror is reflecting, it is called a concave mirror.
→ Convex mirror: If the outer surface of the spherical mirror is reflecting, it is called a convex mirror.
→ Light Reflection: The bouncing back of light after when light strikes a smooth surface.
→ Refraction of Light: When a ray of light enters from one transparent medium to another transparent medium, the ray of light changes its path. The phenomenon of change of path by light is called refraction.
→ Convex lens: This is a piece of transparent shell that is thicker in the middle than the edges. It is also called a converging lens.
→ Concave lens: This is a piece of the transparent medium that is thin in the middle and thick at the edges. This lens is also called a diverging lens.
→ Focus: The point on the principal axis where the parallel rays of light meet or appear to meet after passing through the lens is called the focus.
→ Focal length: The distance between the principal focus and the center of the lens is called the focal length of the lens.
→ Splitting of light: The process of splitting by when white light passes through a transparent medium (such as a prism of glass) of white light into seven colours is called the splitting of light.
→ Spectrum: It is a band of seven colours obtained after passing white light through the prism. These colors from top to bottom are Violet, Indigo, Blue, Green, Yellow, Orange, and Red.