CBSE Class 8 Science Light Chapter Notes

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Light

Light
Light is a form of energy which produces the sensation of sight. Light is electromagnetic wave which does not require any material medium for its propagation. The speed of light waves depend on the nature of the medium through which they pass.

Reflection of Light
The process of bouncing back of the light to the same medium after striking the surface of another medium is called reflection.
A surface which reflects the light is called reflector. Silver metal is one of the best reflectors of light. A highly polished surface, such as a mirror, reflects most of the light falling on it.

Types of reflection: There are two types of reflection

Regular Reflection: When a parallel beam of light falls on a smooth and highly polished surface, then the reflected beam is also parallel and directed in a fixed direction. Such type of reflection is called regular reflection. For example, light reflected from search light, automobile head lights, etc.

Diffused Reflection: When a parallel beam of light falls on a rough surface, then the reflected light is not parallel but spreads in all directions, such type of reflection of light is called irregular or diffused reflection. For example, light reflected from the wooden surface.

Laws of Reflection
The reflection of light from a plane surface or from a spherical surface takes place according to two laws which are:
i) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.

ii)The angle of incidence is equal to the angle of reflection (i.e., Ði = Ðr). 

These laws of reflection are applicable to all types of reflecting surfaces such as plane surface, spherical surfaces or any irregular surface.

Formation of Image by Plane Mirror
Consider a point object O placed infront of a plane mirror MM´. The mirror will form an image I of the object O. Here, two reflected rays AB and CO when produced backward, they meet at a point behind the mirror and hence form the virtual image I at that point

Properties of Images formed by a Plane Mirror
i) The image formed by a plane mirror is virtual and erect.
ii) The distance of the object from the mirror is equal to the distance of the image from the mirror.
iii) The size of the image is equal to the size of the object.
iv) The linear magnification produced by a plane mirror is unity. i.e., m = v/u= h'/h=1
v) The image formed is laterally inverted, i.e., the left side of the image appears to the right side and viceversa.

Uses of Plane Mirror
i) Plane mirror is used as a looking glass.
ii) Plane mirror is used in solar cooker to reflect the sun light.
iii) Plane mirrors are used in periscopes usually used in submarines.
iv) Plane mirros are used in barber’s shop to see the back portion of the head.

In the following videos we have explained you about the concept of Light and its properties. Watch this video to understand the concepts and also post your questions and comments in the comments section

Part 1

Part 2

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