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Light Questions and answers for Class 8

In this page we have Light Class 8 Practice Questions CBSE . Hope you like them and do not forget to like , social share and comment at the end of the page.

Fill in the blanks

(1) The ________ at the point of incidence is called the normal.
(2) __________ is a light sensitive screen
(3) When two mirrors are kept parallel to each other the number of images is _____________.
(4) Kaleidoscope works on the principle of __________.
(5) The splitting of white light into its constituent colours is called ________.
(6) The coloured part of eye is _________.
(7) The ________muscles alter the ________ of the eye lens.
(8) The normal value for a ________ is approximately 25cm.
(9) Droplets of water split sunlight to form a spectrum known as ______.
(10) ________ can be corrected by using a concave lens of suitable focal length.
(11) Refraction occurs because the ________ of light is different in different medium.
(12) When white light passes through a prism, it is __________.
(13) In a Kaleidoscope, the mirrors make an angle of _______ with each other.
(14) The English Braille system uses _________ dots.
(15) Lateral displacement takes place due to refraction in a ________.

Answer

(1) Perpendicular
(2) Retina
(3) Infinite
(4) Multiple reflection
(5) Dispersion
(6) Iris
(7) Ciliary, thickness
(8) Near point
(9) Rainbow
(10) Myopia
(11) Speed
(12) Deviated and dispersed
(13) 60o
(14) 6
(15) Rectangular slab

Short Answer Questions

Question 1
What is virtual image?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

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?

Answer

(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?

Answer

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?

Answer

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

Practice Question

Question 1.
What do you mean by lateral inversion?

Question 2.
How will you experimentally locate the image of an object made by a plane mirror?

Question 3.
Draw a ray diagram to locate the image of an object placed 5 cm in front of a plane mirror?

Question 4.
Differentiate between regular and diffused reflection. Draw diagram to show the two types of reflection?

Question 5.
State three uses of plane mirrors

Question 6.
What is Kaleidoscope? State the principle on which it is based?

Question 7.
Distinguish between myopia and hypermetropia?

Question 8.

Question 9.
Explain persistence of vision?

Question 10.
With the help of neat illustrations, describe the principle focus of spherical lenses?

Question 11.
How is rainbow formed?

Question 12.
What is the blind spot? where it is located?

Question 13.
Describe, giving reasons, the path of a ray of light incident on a glass slab takes till it emerges from the slab?

Question 14.
What do you mean by accommodation of the eye? What gives the eye the power of accommodation?

Question 15.
A coin kept at the bottom of a glass bowl full of water appears to be higher than it actually is? With the help of labeled diagram, explain why this happen?

Multiple Choice Questions

Question 1.
Which of the following statements is correct regarding rods and cones in the human eye?
(a) Cones are sensitive to dim light.
(b) Cones are sensitive to bright light.
(c) Rods are sensitive to bright light.
(d) Rods can sense colour.

Question 2.
Magnification produced by a plane mirror is
(a)-1
(b) zero
(c) +1
(d) infinity

Question 3.
The splitting of light into its component colours is termed as
(a) refraction of light
(b)spectrum
(c) diffraction of light
(d) dispertion of light

Question 4.
If the angle of incident is 30° , what will be the angle of reflection from plane mirror
(a) 30°
(b) 90°
(c) 60°
(d) 0°

Question 5.
Part of the eye which controls the light entering is called
(a) iris
(b) cornea
(c) retina
(d) lens

Question 6.
An object 10cm high is placed at a distance of 50 cm from a plane mirror .The size of the image will be.
(a) 20 cm
(b) 40cm
(c) 10cm
(d) 100cm

Question 7.
The visually impaired can also read with fingers using a special alphabet called :-
a. Bralle
b. Brialle
c. Brallie
d. Braille

Question 8.
Image formed by the plane mirror is:
(a) Always real
(b) Always virtual
(c) Sometimes real sometimes virtual
(d) None of these

Question 9.
The type of lens in Human eye is
a. Convex
b. concave
c. Mixture
d. None of these

Question 10.
The property of plane mirror to make 'right appear as left' and vice versa, is called:
(a) Vertical inversion
(b) Refraction
(c) Reflection
(d) Lateral inversion

Answer

1. b
2. c
3. d
4. a
5. a
6. c
7. d
8. b
9. a
10.d

Summary

This light class 8 questions and answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.

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