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Page No 208:

Question 1:

The angle of incidence is
(a) the angle that the incident ray makes with the mirror
(b) the angle that the incident ray makes with the normal at the point of incidence
(c) 180° minus the angle that the incident ray makes with the mirror
(d) the angle that the incident ray makes with the reflected ray

Answer:

(b) the angle that the incident ray makes with the normal at the point of incidence
The angle of incidence is the angle made by an incident ray with the normal at the point of incidence.

Page No 208:

Question 2:

If you stand in front of a plane mirror and scratch your left cheek, your image
(a) scratches its left cheek.
(b) scratches its right cheek.
(c) scratches both cheeks one by one.
(d) does not scratch at all.

Answer:

 (b) scratches its right cheek

In a plane mirror, the image is laterally inverted. 

Page No 208:

Question 3:

The image formed by a plane mirror is
(a) virtual, erect, behind the mirror and smaller than the object.
(b) virtual, erect, behind the mirror and the same size as the object.
(c) virtual, inverted, behind the mirror and the same size as the object.
(d) real, erect, behind the mirror and the same size as the object.

Answer:

 (b) virtual, erect, behind the mirror and of the same size as the object

Image formed by a plane mirror is always virtual, erect, behind the mirror and of the same size as the object.

Page No 208:

Question 4:

If the angle between the mirror and the incident ray is 30°, the angle of reflection is
(a) 30°.
(b) 60°.
(c) 15°.
(d) 90°.

Answer:

 (b) 60⁰

Incident angle = Angle of reflection
Incident angle = 90° - 30° = 60° = Angle of reflection

Page No 208:

Question 5:

The image formed by a plane mirror is formed
(a) on the surface of the mirror.
(b) just in front of the mirror.
(c) just behind the mirror.
(d) as much behind the mirror as the object is in front of the mirror.

Answer:

(d) as much behind the mirror as the object is in front of the mirror.
The image formed by a plane mirror is formed as much behind the mirror as the object is in front of the mirror.

Page No 208:

Question 6:

Two plane mirrors are kept at the following angles one by one. In which case is the number of images formed maximum?
(a) 30°
(b) 60°
(c) 45°
(d) 90°

Answer:

 (a) 30⁰

When two plane mirrors are inclined to each other at an angle of 30⁰, the number of images formed is maximum.

Page No 208:

Question 1:

Is the reflection of light by the smooth walls of your house regular or irregular?

Answer:

The reflection of light from the walls of our house is irregular, as at the microscopic level, their surfaces are not smooth. This is known as diffuse reflection. The roughness or smoothness of a surface, even if it is microscopical, tremendously affects the subsequent reflection of a beam of light.

Page No 208:

Question 2:

A plane mirror always forms the image of an object exactly on the reflecting surface. True or false?

Answer:

True.
A plane mirror always forms a virtual image, i.e., the rays of light from the object don't actually form the image; but these are the extensions of the reflected light rays that appear to intersect behind the mirror. Hence, the image is formed on the reflecting surface. 

Page No 208:

Question 3:

Is the image formed by a plane mirror exactly of the same size as the object?

Answer:

Yes, the image formed by a plane mirror is always virtual, erect, behind the mirror and of the same size as the object.

Page No 208:

Question 4:

The image formed by a plane mirror is always erect. True or false?

Answer:

True
The image formed by a plane mirror is always virtual, erect, behind the mirror and of the same size as the object.

Page No 208:

Question 5:

If angle of  incidence of a ray on a plane mirror is 60°, what is the angle of reflection?

Answer:

In optics, the angle of incidence is equal to the angle of reflection. Therefore, the angle of reflection will also be 60°.

Page No 208:

Question 6:

The angle of incidence of a ray on a mirror is the angle that the ray makes with the mirror at the point of incidence. True or false?

Answer:

False. The angle of incidence is the angle made by an incident ray with a perpendicular to the mirror at the point of incidence.

Page No 208:

Question 7:

Two plane mirrors kept at 60° form __________ images of an object kept between them.

Answer:

Two plane mirrors kept at 60° form 5 images of an object kept between them.

The number of images formed by two plane mirrors kept at a particular angle are as follows:
n = [(360°/Θ) - 1 ] when (360°/Θ) is even integer, and
n = (360°/Θ) when (360°/Θ) is odd integer
Here, Θ is the angle between the two mirrors.
Therefore, the number of images formed (n) = [(360°/60°) - 1 ] = [6 - 1] = 5

Page No 208:

Question 8:

In a kaleidoscope, the mirrors make an angle of __________ with each other.

Answer:

 In a kaleidoscope, the mirrors make an angle of  60° with each other.

Page No 208:

Question 1:

What is reflection of light?

Answer:

Reflection of light is the phenomenon in which a ray of light bounces back after striking a surface.



Page No 209:

Question 1:

List the main characteristics of the image formed by a plane mirror.

Answer:

 The main characteristics of an image formed by a plane mirror are as follows:
1. It forms a virtual image.
2. Image is formed behind the mirror.
3. Image is erect.
4. Image is of the same size as the object.
5. Image is at the same distance behind the mirror as the object is in front of the mirror.

Page No 209:

Question 2:

State three uses of a plane mirror.

Answer:

Three uses of a plane mirror are:
1) Plane mirrors are mostly used to reflect light on an object.
2) Plane mirrors are also used in scientific apparatus like telescopes and periscopes.
3) Plane mirrors are also used in kaleidoscopes for producing symmetrical patterns through multiple reflections from inclined mirrors enclosed in a tube.

Page No 209:

Question 3:

Two mirror are kept perpendicular to each other. A ray strikes one mirror at an angle of 45° to the normal. Find the direction of the ray after reflection by the second mirror, by drawing a ray diagram.

Answer:



Here, i1 = r1 = i2  = r2 = 450

Page No 209:

Question 1:

In which direction will a light ray falling along the normal to a mirror be reflected?

Answer:

The angle of incidence is equal to the angle of reflection. If the incident ray falls along the normal to a surface, it will be reflected along the normal i.e., the right ray will retrace its path.

Page No 209:

Question 2:

A ray incident on a plane mirror is reflected in a direction such that the angle between the incident and the reflected ray is 90°. What are the angles of incidence and reflection?

Answer:

 The law of reflection states that the angle of reflection is equal to the angle of incidence.
i.e.,  i + r = 900  (given)....... (1)
where, i and r have their usual meaning
Therefore, from the law of reflection, i = r 
Now, putting it in equation (1)
=> i + i = 900
=> i = 450
=> r = i = 450

Page No 209:

Question 3:

If all objects around us were to reflect light in a regular way, what problems might we face?

Answer:

Irregular reflection is what enables us to see all the objects around us. But, in case of a regular reflection, every object would have acted as a mirror thereby illuminating the surroundings. This would have a blinding effect on our eyes making it harder for us to see things around us.

Page No 209:

Question 4:

A boy is standing at a distance of 4 m in front of a mirror. He moves 2 m towards the mirror. In which direction will the image move−towards the mirror or away from it?

Answer:

In a plane mirror, the image is formed at the same distance behind the mirror as the object is in front of it. Hence, when the boy moves towards the mirror, his image will also move towards it by the same distance.

Page No 209:

Question 5:

In the figure shown below, MN is a plane mirror. W, X, Y and Z are four children. Mark the positions of the reflections of W, X, Y and Z in the mirror. Answer the following questions.
(a) Which child/children can see their own images in the mirror?
(b) Can child W are see images of X, Y and Z in the mirror?

Answer:

 The reflections of  W, X, Y and Z are as follows:

The boy 'Z' will have no reflection, as the incident ray from him is parallel to the plane of the mirror.

(a) Only X will be able to see his own image.
(b) W can see the reflections of X and Y but not Z, as the incident ray from Z is parallel to the plane of the mirror.

Page No 209:

Question 6:

Can the image formed by a plane mirror be projected on to a screen?

Answer:

No, the image formed in a plane mirror cannot be projected on a screen, as it is a virtual image. Only real images can be projected on a screen.

Page No 209:

Question 7:

The image of an object is formed by two plane mirrors. One of the mirrors is double the size of the other. In which case will the image be bigger? Why?

Answer:

The image formed by a plane mirror is always virtual, erect, behind the mirror and of the same size as the object. The size of the image is independent of the size of the plane mirror. Hence, the image in both the mirrors will be of the same size.

Page No 209:

Question 2:

What is the second law of reflection?

Answer:

The second law of reflection states that incident ray, normal and reflected ray all lies in the same plane.

Page No 209:

Question 3:

What is lateral inversion?

Answer:

Lateral inversion is a type of reversal that occurs with an image formed by a plane mirror. For example, if a person raises his/her right hand, his/her image in the mirror will show the left hand up.

Page No 209:

Question 4:

Draw the image of the letter 'B' as formed by a plane mirror placed on the right side of 'B'.

Answer:

 The image of the letter 'B' as formed by a plane mirror placed on the right side of 'B' is as follows:

Page No 209:

Question 5:

What is the function of a periscope in a submarine?

Answer:

The periscope of a submarine helps its crew to locate any object or enemy ship on the surface of the sea.

Page No 209:

Question 1:

Differentiate between regular and diffused reflection. Draw diagrams to show the two types of reflections.

Answer:

 

Regular reflection Diffused reflection
It takes place on a smooth surface where the entire beam is reflected in only one direction. It takes place on a rough surface where the beams of light are reflected in different directions.

Page No 209:

Question 2:

State the first law of reflection, and show it by a labelled diagram.

Answer:

The first law of reflection states that the angle of incident is equal to the angle of reflection.

Page No 209:

Question 3:

Why are multiple images formed when two mirrors are placed at right angles to each other?

Answer:

When two mirrors are placed at a right angle to each other, multiple images are formed due to multiple reflections. The image formed by the first mirror acts as the object for the second mirror.

Page No 209:

Question 4:

Calculate the number of images formed by plane mirrors kept at an angle of 10° to each other.

Answer:

The number of images formed by two plane mirrors kept at an angle of 10° to each other can be given by:
n = [(360°/Θ) - 1 ]
Therefore, the number of images formed (n) = [(360°/10°) - 1 ] = [36 - 1] = 35

Page No 209:

Question 5:

What is a kaleidoscope? State the principle on which it is based.

Answer:

A kaleidoscope is a tube-shaped optical instrument that is rotated to produce a succession of symmetrical designs by means of multiple mirror reflections. The constantly changing patterns are made by bits of coloured glasses present at one end of the tube. The kaleidoscope operates on the principle of multiple reflections, where several mirrors are placed at an angle of 60°(usually) to one another.



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