Light Extra Questions for Chapter 13 Class 8

(i)Objects that can emit light energy by themselves are known as luminous object and objects that cannot emit light energy by themselves are known as non-luminous objects.
(ii)The angle of incidence is the angle between the normal and the incident ray.
(iii)When light falls on a smooth uniform surface, all the parallel incident rays are reflected perfectly parallel is known as regular reflection of light.
(iv)There are seven colours present in white light like, red, orange, yellow, green, blue, indigo, and violet.
(v)Tactual aids are non-optical sensory aids which involve the use of touch.

(a)II
(b)III
(c)III
(d)IV
(e)II

(a) -> iii
(b) -> iv
(c) -> ii
(d) ->i
(e) -> v

There are two type of law of reflection:
(1) The incident ray, the reflected ray and the normal, all lie in the same plane.
(2) The angle of incidence is equal to the angle of reflection.

There are two type of reflection:
(1) Regular : In regular Reflection, light reflected from a smooth surface in a definite direction. (2) Irregular: In irregular reflection, light reflected from a rough surface in all directions and not in a definite direction.

A kaleidoscope is an optical instrument consisting of two or more reflecting surfaces. These surfaces tilted towards each other at a certain angle to obtain symmetrical patterns when viewed from the other end.

Ambulance is written opposite on the Ambulance because of the lateral inversion property of mirrors. As the property describes, left becomes right and right becomes left. Therefore, if anyone sees the Ambulance in the mirror, it looks correct.

A periscope is a long, tabular device through which a person can see objects that are out of the direct line of sight. It is used in submarine navigation and in land and sea warfare.

Power of accommodation is the ability of the eye lens to focus near and far objects clearly on the retina by adjusting its focal length.

When we see a faraway object, the ciliary muscles relax and flatten the lens so that its focal length increases. Thus, while seeing distant objects we never feel any strain on the eye.

Cataract is an eye disease generally occur at the old age. Sometimes due to the formation of a membrane over the crystalline lens of some people in the old age, the eye lens becomes hazy or even opaque. It results in decrease or loss in vision of the eye.

Place an object between the mirrors. You can see several images in both the mirror. This is because the image formed by one mirror acts as the object for the second mirror. This phenomenon is referred to as multiple reflections.
The no. of images formed depends on the angle between the mirrors. The formula used for finding the no. of images are $n= 360 \div \theta -1$ Where n is the no. of images and is the angle between the two mirrors.

Braille is a system developed by Louis Braille in 1824 to help visually challenged people. It is a code by which languages such as English, French, Spanish, etc. can be written and read. This code consists of raised dots, that can be read with fingers by blind people. It is a widely used system across the globe and is a very important invention. Braille symbols are represented inside units of space known as Braille cells. A full cell consists of a set of six raised dots arranged in the form of a 2*3 matrices. 64 different combinations can be created by using one or more dots. Each cell is used to represent an alphabet, a number, a punctuation mark, or a special symbol.