Light Class 8 Science Short Answer question CBSE

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SHORT Answer Question

Question 1
What is virtual image?

When the incident and reflected rays do not actually meet at the image and     the image can not be formed on a screen then this is virtual image.

Question 2
What are the characteristics of the image formed by a plane mirror?

The image formed by plane mirror is erect, virtual same size as the object, laterally inverted.

Question 3
What is the function of a periscope in a submarine?

From a submarine under the sea, a sailor can see objects and enemy ships on the surface of the sea by using a periscope.

Question 4
Calculate the number of images formed by plane mirror kept an angle of 30o to each other?

Number of images formed is given by the formula –
                                  n = 360/0 -1
                                    n = 360/30 -1
                                     n = 12 – 1
                                     n = 11 images

Question 5
What is the main structural difference between a convex and a concave mirror?

The convex mirror is bulging out from the middle while the concave lens bulging out from the edges.

Question 6
What is the aperture of a lens?

 Aperture of lens is a point from where the reflection of light takes place.

Question 7

For a proper in take of Vitamin A, what kind of food should you eat?

Vitamin A helps to improve eyesight so we should have vitamin A rich diet which includes pumpkin, mangoes, carrot, yam, dairy products, eggs and fish.

Question 8

What is the cause of refraction?

Refraction is caused by the change of speed of light when it passes from one medium to another.

Question 9

Stars appear to be slightly higher in the sky than they actually are, Why is this so?

The air in the atmosphere consists of different layers of different densitiesThe density is maximum near the surface of EarthRefraction takes place at the surface of each layerBecause of atmosphere refraction all stars except those directly overhead, appeared slightly above the horizon than they really are.

Question 10
Distinguish between near point and far point of eye?

The least distance at which the eye can see an object clearly is called the near point of the eyeWhile the far point of the eye is the maximum distance at which it can see clearlyFor a normal eye, it is at infinity.

Question 11
What are the differences between reflection and refraction of light?
 When light ray strike on opaque surface and rebound into the same medium, reflection occursWhile Refraction occurs when a ray of light passes from one transparent to another having different densities.

Question 12
Give reasons-
a) A concave lens is also known as a diverging lens?
b) An object seen through a prison appears coloured.
c) It is not possible to see an object clearly if it is kept too close to the eye?
(a) In the case of concave lens the rays of light do not actually meet but appear to diverge from a point called principle focusIt has the property of bending a ray of light passing through it outwards.
(b) Because beam of light after passing through a prison formed a bend of seven colours called spectrum.
(c)We are able to see an image only if it is formed on the retinaIf the image is focused in form or behind the retina, the image appeared to be blurred.

Question 13

Distinguish between converging and diverging lens?
Converging lens:-
 A converging (convex) lens is thick in the middle and become thinner at the edges.
 A converging lens bends a ray of light passing through it inwards.
Diverging lens:
 A diverging (concave) lens is thin at the middle and thicker at the edges.
 Diverging lens bends a ray of light passing through it outwards.

Question 14
Why a pencil dipped in water appear bent at the surface of water?

A pencil dipped in water appears bent at the surface of water because of refraction.

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