# RBSE Solutions for Class 7 Science Chapter 14 Reflection of Light

## Rajasthan Board RBSE Class 7 Science Chapter 14 Reflection of Light

RBSE Solutions for Class 7 Science

### RBSE Class 7 Science Reflection of Light Intext Questions and Answers

Page No 133.

Question 1.
Here are given angles of incidence with normal. Note down the values of reflected angles in table. Angles of incidence are

1. 25°
2. 30°
3. 35°
4. 40°
5. 45°

Answer:
Table : Angles of incidence & angle of reflection:

page No 136.

Question 2.
How many images are formed when an object is placed between two parallel mirrors?
Answer:
infinite number of Images are formed of an object placed between two parallel mirrors.

Question 3.
If the mirrors are positioned at any angle to each other and an object is placed are between them, then how many images of an object will be formed ?
Answer:
Number of images (N) =

can get no. of images by using this formulae.

Question 4.
Find out the number of images formed by the two mirrors at different angles to each other as given in table. Divide 360° by angle θ and deduct one from it. Is this value equal to number of images formed ?
Answer:
Table

page No 138.

Question 5.
If the reflecting surface is not plane but it ¡s curved then what kind of images formation take place ?
Answer:
If the reflecting surface is curved, then these can be of two types

1. Concave mirror – This has inwardly depressed curved surface. This forms inverted, real and small sized image.
2. Convex mirror – Any outwardly bulging curved surface is called convex. This forms erect, virtual and small sized image.

Question 6.
What are the shapes of concave & convex mirrors ?
Answer:
Concave mirror has inwardly depressed curved surface while convex mirror has outwardly bulging curved surface,

### RBSE Class 7 Science Reflection of Light Text Book Questions and Answers

Choose the appropriate option:

Question 1.
Image formed by concave mirror for an object placed away from centre curvature is –

(a) At centre of curvature
(b) at a focal point
(c) at an infinity
(d) between focal point and centre of radius curvature
Answer:
(d) between focal point and centre of radius curvature

Question 2.
To see the rear view of vehicles the following is used –
(a) Convex mirror
(b) Concave mirror
(c) Plane mirror
(d) All the above
Answer:
(b) Concave mirror

Question 3.
Image formed for an object placed in front of a plane mirror is –
(a) At distance equal to distance between object and the plane mirror
(b) At twice the distance
(c) At half the distance
(d) At four times the distance
Answer:
(a) At distance equal to distance between object and the plane mirror

Fill in the blanks:

1. Image formed b convex mirror is erect, small ………………………..
2. Infinite number of images are formed by two plane mirrors having ……………………….. angle in between them.
3. We use ……………………….. mirror to see our image.

Answer:

1. Virtual
2. Zero
3. Concave.

Short Answer Questions:

Question 1.
Define reflection.
Answer:
The reflection of light-rays after striking a bright surface or a mirror back in the same medium is called reflection of light.

Question 2.
A concave mirror has focal length of 20 cm. Calculate its radius of curvature.
Answer:
Radius of curvature (R) = Focal length
(f) x 2
R = 20 x 2
R = 40 cm

Question 3.
Write down the laws of reflection.
Answer:
Following arc the laws of reflection –

1. First Law – The angle of incidence is equal to the angle to reflection. i.e. Angle of incidence (i) = angle of reflection (r)
2. Second Law – Incident ray, reflected ray and perpendicular. lie in the same plane.

Question 4.
What will you call the right part of an object image as left-part by plane mirror ?
Answer:
In a plane mirror, left part of the object is seen as right in image and right part is seen as left in image. This phenomenon is called lateral transformation.

Question 5.
What is the difference between concave and convex mirror on the basis of constitution and image formation ?
Answer:
Difference between concave and convex mirror –

Long Answer type Questions:

Question 1.
Explain the process of image. formation with a diagram for an object placed in front of a plane mirror.
Answer:
Reflection from a plane mirror –

Experiment:
Place a vertical plane mirror in between a thermocol as shown in figure. Place a pencil in vertical position at a little distance in front of the mirror. See its image in the mirror. Now place the pencil at different positions in front of the mirror and each case see the position of image. By seeing the image formed we come to know that image formed b a plane mirror is upright and is equal in size to the object. Also image formed behind the mirror is at a distance equal to the distance of object from the mirror.

Question 2.
Differentiate between virtual and real images.
Answer:
Real image:
Image formed at any point which can be taken on screen is called real image.

Virtual Image:
These images seem to form at a point but practically no image is formed at that point. This image can not be obtained on screen,

Question 3.
Explain the regular and diffused reflection with the help of a diagram.
Answer:
1. Regular reflection:
When parallel rays of light are incident on plane mirror then reflected rays are parallel to each other in any specific direction. This type of reflection is called regular reflection. Regular reflection occurs by plane mirrors or other smooth and bright surfaces.

2. Diffused reflection:
When the incident rays fall on a rough surface they are parallel to each other but after reflection they are no longer parallel but are reflected in different directions. This type of irregular reflection is called diffused‘ reflection. Diffused reflection is caused by irregular surface of the reflector. Diffused reflection occurs on the irregular surfaces such as – books, surface of table, etc. The presence of light under a tree and inside the room is because of diffused reflection.

### RBSE Class 7 Science Reflection of Light Important Questions and Answers

Objective Questions:

Question 1.
Angle between incident ray and reflected ray is called –
(a) Angle of reflection
(b) Angle of incidence
(c) Right angle
(d) All the above
Answer:
(b) Angle of incidence

Question 2.
How is the reflector surface in diffused reflection –
(a) Smooth
(b) Plane
(c) Irregular
(d) None of these
Answer:
(c) Irregular

Question 3.
Image that can not be obtained on screen is –
(a) Virtual image
(b) Real image
(c) both (a) & (b)
(d) None of two
Answer:
(a) Virtual image

Question 4.
How many images are formed of an object placed between two parallel mirrors –
(a) Infinite
(b) Two
(c) Three
(d) Four
Answer:
(a) Infinite

Question 5.
Which type of mirrors are used in side glass of vehicles –
(a) Concave mirror
(b) Convex mirror
(c) both (a) & (b)
(d) None of the two
Answer:
(b) Convex mirror

Question 6.
Light always travel in –
(a) Straight line
(b) Curved line
(c) Not move
(d) Any line
Answer:
(a) Straight line

Question 7.
Angle of incidence and angle of reflection are always –
(a) Changeable
(b) Equal
(c) Less & more
(d) Less
Answer:
(b) Equal

Question 8.
Image that can not be obtained on screen, is called –
(a) Real
(b) Virtual
(c) both (a) & (b)
(d) None of two
Answer:
(b) Virtual

Question 9.
Image that can not be obtained on screen is called –
(a) Real
(b) Virtual
(c) both a & b
(d) None of two
Answer:
(a) Real

Fill in the Blanks:

1. Angle formed between reflected ray and perpendicular is called ………………………. (angle of reflection / angle of incidence)
2. Irregular reflection is called ………………………. (Regular / Diffused).
3. Image formed by plane mirror is ………………………. (inverted / erect).
4. Spherical mirrors are of two types ………………………. and ………………………. (Concave mirror, convex mirror / plane mirror, curved).
5. Mirrors which have spherical reflector surface are called ………………………. (Spherical / Plane )
Answer:

1. Angle of reflection
2. diffused.
3. Erect
4. Concave mirror, convex mirror
5. Spherical.

Match the column I with column II –

Question 1.

Answer:

1. (b)
2. (c)
3. (a)
4. (e)
5. (d).

Very Short Answer Type Questions:

Question 1.
What is called incident ray ?
Answer:
The rays coming from light source and striking on mirror, are called incident ray.

Question 2.
What is reflected ray ?
Answer:
The ray returning back into the same medium after reflection from mirror surface is called reflected ray.

Question 3.
What is angle of incidence ?
Answer:
Angle formed between incidence ray and perpendicular, is called angle of incidence.

Question 4.
What is angle of reflection ?
Answer:
Angle formed between reflected ray and perpendicular.

Question 5.
How are angle of reflection and angle of incidence related ?
Answer:
These are always equal.

Question 6.
What is second law of reflection ?
Answer:
Incidence ray, reflected ray and perpendicular. all lie in same plane. It is called second law of reflection.

Question 7.
What do you mean by regular reflection and on which surfaces it occurs ?
Answer:
When parallel rays of light are incident on a plane mirror then the reflected rays of light are also parallel to each other, It is called regular reflection. It occurs from smooth and plane surfaces.

Question 8.
What is called diffused reflection and on which surfaces it occurs ?
Answer:
The parallel light rays incident on ail irregular surface after being reflected are not parallel to each other but are reflected in different directions. It is called diffused reflection. It occurs from irregular / rough surfaces.

Question 9.
What are effects / functions of diffused reflection ?
Answer:
The presence of light under a tree and inside the room is because of diffused reflection.

Question 10.
Which type of image is formed by plane mirror ?
Answer:
Erect and same sized image is formed by plane mirror

Question 11.
Where is image formed in plane mirror ?
Answer:
Behind the plane mirror. image is formed and at a distance equal to the distance of object from the mirror.

Question 12.
What is meant by partial reflector?
Answer:
Surfaces which can reflect a part of light incident on it. are called partial reflector surfaces.

Question 13.
What is virtual image?
Answer:
The image which can not be obtained on screen is called virtual image. These images seem to form at a point and practically no image is formed at that point.

Question 14.
What is called real image ?
Answer:
The images that are really formed at ally point and which an be obtained on screen. are called real images.

Question 15.
What is meant by lateral transformation ?
Answer:
in plane mirrors left part of the object is seen as right in image and right part is seen as left in image. This phenomenon is called lateral transformation.

Question 16.
How many images are formed of an object placed between two parallel plane mirrors?
Answer:
Infinite images are formed.

Question 17.
Write the formulae to calculate the number of images formed of an object placed between two plane mirrors which are oblique to each other by an angle (O).
Answer:
Number of images (N)

Question 18.
What is spherical mirror ?
Answer:
Mirrors having curved surfaces for reflection are called spherical mirrors.

Question 19.
Write names of types of Spherical mirrors ?
Answer:
Spherical mirrors arc of two types:

• Concave (convergent)
• convex (divergent) mirror.

Question 20.
What is concave mirror ?
Answer:
The bulged inward part i.e. the centre of the spherical mirror works as reflector is called concave mirror.

Question 21.
What is convex mirror ?
Answer:
A spherical mirror in which the outwardly curved part works as reflector is called convex mirror.

Question 22.
Why concave mirror is called convergent mirror also ?
Answer:
The parallel rays coming from the Sun are converged as a bright sharp spot by a concave mirror. So it is also called as convergent mirror.

Question 23.
Why a convex mirror is called divergent mirror ?
Answer:
The parallel rays coming from the Sun are not converged at spot by the convex mirror but are spread (diverged). That is why, the convex mirror is called a Divergent mirror.

Question 24.
What is called centre of curvature of a spherical mirror ?
Answer:
The reflector surface of a spherical mirror is the part of a sphere. The centre of this sphere is called centre of curvature.

Question 25.
What is called radius of curvature of a spherical mirror?
Answer:
The radius of a sphere whose part is the spherical mirror, is called radius of curvature.

Question 26.
What is called pole of a spherical mirror?
Answer:
The centre ‘O’ of reflecting surface of spherical mirror is called pole.

Question 27.
What is called principle axis of spherical mirror ?
Answer:
The Line Joining the pole ‘O and centre of curvature C of the mirror is called Principle axis.

Question 28.
What is called focus of a concave mirror?
Answer:
After reflection. incident rays parallel to principle axis are concentrated on a point on the principle axis. This point is called as Focus (F) of the concave mirror.

Question 29.
What is called focus of a convex mirror?
Answer:
Incident rays from a convex mirror parallel to principle axis seem to come from a point on principle axis after reflection. This point is called Focus of convex mirror.

Short Answer type Questions:

Question 1.
What are called complete and partial reflectors ?
Answer:
Complete Reflectors – Those surfaces which reflect most of incident light rays that fall on it arc called complete I good reflectors. eg. smooth and polished surface of an object, mirror. etc. Partial Reflectors : Those surfaces which reflex only a small amount of incident light rays are called partial / moderate reflectors. eg. rough surfaces.

Question 2.
What are angle of incident and angle of reflection ? What is relationship between them?
Answer:

• Angle of incidence : Angle formed between incident ray and perpendicular (i).
• Angle of reflection (r) : Angle formed between reflected ray and perpendicular is called angle or reflection.

Relationship –
Angle of incident (i) is always equal to angle of reflection (r).

Question 3.
Explain the lateral transformation.
Answer:
In plane mirror the left part appears as right in the image and right part appears as left in the image. This phenomenon is called Lateral transformation. Due to lateral transformation, words are written in a specific manner at the front side of ambulance so that image formed in side glass of the vehicle ahead of the ambulance is accurate and the driver of the vehicle views it as AMBULANCE and will easily give side to the ambulance to overtake it.

Question 4.
Differentiate between regular and diffused reflection ?
Answer:
Difference between regular & diffused reflection:

Question 5.
Concave mirror is also called convergent mirror. Why ? Draw diagram also.
Answer:
The parallel rays coming from the Sun are converged as a bright sharp spot by a concave mirror. So it is also called as convergent mirror. Actually, bright spot of light on paper sheet is the image of the Sun.

Question 6.
State the characteristics of image formed by plane mirror.
Answer:
Following are the characteristics of images formed by plane mirror:

• Image formed by plane mirror is always virtual & upright.
• Size of image and object size is always equal.
• Image formed behind the mirror is at a distance equal to the distance of object from the mirror.
• Lateral transformation occurs in image.

Question 7.
Explain the spherical mirrors by diagram.
Answer:
Spherical mirrors are of two types –

• Concave mirror – A spherical mirror n which the inwardly curved part works as reflector is called concave mirror.
• Convex mirror – A spherical mirror in which the outwardly curved part works as reflector is called convex mirror.

Question 8.
What is image ? How many types of images are ?
Answer:
Image:
When we place any object in front of a mirror, then the figure of that object is formed in the mirror. This figure formed in mirror of that object is called image of that object. Hence, it can also be said that light rays coming from a point of object meet at a point after reflection, then the .second point is called image of first point. Images are of two types –

• Real image
• Virtual image.

Question 9.
Why convex mirror is – called divergent mirror. Explain with diagram by an experiment.
Answer:
Experiment:
Hold a convex mirror in your hand and face its reflecting surface towards the sun. Focus the light reflected from the mirror on a black paper sheet placed near the mirror. Gradually move the paper sheet back ward and forward. We see that the parallel rays coming from sun are not converged at spot by the convex mirror but arc spread (diverged). That is why. the convex mirror is called a divergent mirror.

Question 10.
State the uses of concave mirror.
Answer:

• Generally concave mirrors are used in torch. search lights and headlights of vehicles to obtain a powerful beam of parallel light.
• Concave mirrors are used to obtain large and clear image for showing.
• Large sized concave mirrors are used to focus sun rays in solar cookers and solar heaters.
• Concave mirrors are used by dentists to view enlarged image of patients teeth.

Question 11.
Write the uses of convex mirrors.
Answer:

1. Convex mirrors are mostly used as side glass of vehicles. These mirrors are clamped at the side of vehicles and driver can view the vehicle at its rear side so that he can drive safely.
2. They form erect image of the object so it is convention.
3. As compared to plane mirror, convex mirrors provide a larger rear view to the driver.

Question 12.
The radius of curvature of a concave mirror is 60 cm. Calculate its focal length.
Answer:
Focal length of concave mirror

f = $$\frac { 60 }{ 2 }$$. (Focal length of concave mirror is half of radius of curvature)
f = 30 cm

Question 13.
Two plane mirrors are placed obliquely at 400 to each other. How many images are formed of an object placed between them ?
Answer:
Number of images =

N = 9 – 1
N = 8 i.e. 8 images will be formed.

Essay Type Questions:

Question 1.
Explains reflection of light with diagram by an experiment.
Answer:
Reflection of light – Experiment :

1. Take a drawing board and fix a white paper with the help of drawing pins.
2. Draw a straight line MN on it b a pencil. Mark a point 0 at the center of MN.
3. Draw a perpendicular line OP on from point ‘O’. OP is called perpendicular.
4. Mark the angle like 90°. 80°, 70°. 10°, 0° on both side of point 0 as shown in figure.
5. Place plane mirror parallel to straight line MN with help of thermocol.
6. Now cover the glass of a torch with black coloured drawing sheet which has a slit in it as shown in figure.
7. Switch on the torch and focus the light passing through slit on the mirror in such a way that it appears as a straight line on the paper. Adjust the position of torch in such a way that its light strikes on the plane mirror with an angle of 25° from the normal OP.
8. Now the light ray reflected back from mirror will also appear on white paper.
9. Put a mark A with pencil on incident light ray
10. Light ray AO that comes from torch and strikes the plane mirror is called incident ray
11. Similarly mark a point C on the reflected light ray. This ray of light that comes back after striking the mirror is called reflected ray (OC).

Question 2.
Only single image is formed by a plane mirror of an object but how many images are formed when the object is placed between the two plane mirrors ? Explain.
Answer:
When we go to a saloon to get a haircut. we sit in front of a plane mirror and another plane mirror is placed at our backside. These two mirrors are parallel to each other. Due to mirror placed at our back. we see multiple images of ourself. Thus, infinite number of images are formed of an object placed between to parallel mirrors.

Question 3.
If the mirrors are positioned at any angle to each other and an object is placed in between them, then how many images of an object will be formed ? Explain by an experiment.
Answer:
Experiment – Make a semicircle on drawing-board with the help of a compass as shown in figure. Mark angles from 0° to 90° on it.

Place two plane mirrors along the lines A. B and C, D in such a way that these mirrors arc at right angles to each other. Now place a pen in between the two mirrors. We observe that three images are formed for an object placed in between mirrors at right angles. Now find out the number of images formed by the two mirrors at different angles to each other. To find out the number of images (N). divide 360° by angle θ and deduct one from it. This value will equal to the number of images of pen formed for that angle.
So. Number of images =

Question 4.
What are spherical mirrors ? How many types are of these ? Explain.
Answer:
Generally most used curved mirrors are spherical mirrors. The reflector surfaces of such mirrors can be assumed to be a part of spherical mirror. Hence such mirrors whose reflector surfaces is spherical are called Spherical mirrors.

• Concave mirror (Convergent mirror)
• Convex mirror (divergent mirror)

These are of two types:

• Concave Mirror – A spherical mirror in which the inwardly curved part works as reflector is called concave mirror.
• Convex mirror – A spherical mirror in which the outwardly curved part works as reflector is called convex mirror.

Question 5.
Explain the Graphical representation of spherical mirrors.
Answer:
Reflecting surfaces for a spherical mirror can be curved towards inside or outside. The graphical representation of these mirrors is shown in figure. In these figures. backside of mirrors is shadowed. Inwardly, curved surface behaves as a concave mirror and outwardly bulged curved surface as a convex mirror. Reflecting surface of a spherical mirror is a part of sphere. Its center C’ is called Radius of Curvature.

The centre ‘O of reflecting surface of spherical mirror is called Pole. The reflecting surface of spherical mirror which is a portion of sphere has Radius (R) which is called the Radius of curvature of mirror. It is shown by ‘OC, The Line Joining the pole O’ and centre of curvature C’ of the mirror is called principle axis.