RBSE Solutions for Class 7 Science Chapter 14 Reflection of Light are part of RBSE Solutions for Class 7 Science. Here we have given Rajasthan Board RBSE Class 7 Science Chapter 14 Reflection of Light.
Board | RBSE |
Textbook | SIERT, Rajasthan |
Class | Class 7 |
Subject | Science |
Chapter | Chapter 14 |
Chapter Name | Reflection of Light |
Number of Questions Solved | 77 |
Category | RBSE Solutions |
Rajasthan Board RBSE Class 7 Science Chapter 14 Reflection of Light
Text book Exercise
Choose the correct answer.
Question 1.
Image formed by concave mirror for a object placed away from centre of curvature is.
(a) at centre of curvature
(b) at focal point
(c) at infinity
(d) in between focal point and centre of radius of curvature
Answer:
(d) in between focal point and centre of radius of 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 these
Answer:
(b) concave mirror
Question 3.
Image formed for an object placed infront of the plane is
(a) at distance equal to distance between object and the plane mirror.
(b) At twice the distance
(c) At half of 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 by convex mirror is erect, small and………………..
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:
- Virtual
- 0°
- Concave
Short Answer Type Questions
Question 1.
Define reflection.
Answer:
The phenomenon of reflection of light rays after colliding with a mirror or any other shiny object back into 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)
= Focus distance x 2 = 20 x 2
= 40
Question 3.
Write down the laws of reflection.
Answer:
The first law of reflection states that, the value of Incident angle and the Reflected angle are always same.
Incident angle (i) = Reflected angle (r)
The second law of reflection states that, incident ray, reflected ray and perpendicular all exist in same plane.
Question 4.
What will you call the right part of an object’s image as left part by plane mirror?
Answer:
In the plane mirror, the left part appears as right in the image and the right part appears as left in the image. This event is called lateral transformation.
Question 5.
What is the difference between concave and convex mirror on the basis of constitution and image formation?
Answer:
The difference between concave and convex mirror is-
Basis | Concave Mirror | Convex Mirror |
Constitution | Spherical mirror in which the outer curved surface works as reflector. | Spherical mirror in which the inner curved surface works as reflector. |
Image Formation |
Image formed is always opposite of the real object | Image formed is always small erect and virtual |
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:
The image formed by a plane mirror is always equal to the size of the virtual, perpendicular and architectural shape. The image is formed at the same distance behind the mirror, as far as the object is placed in front of the mirror. The process of making reflection of the object placed in front of the plane mirror A point of light source ‘O’ is placed in front of a plane mirror MN. Moving from point O, two rays, OA and OC are incident on the mirror as shown in the figure.
Draw a perpendicular points A and C on the surface of mirror MN. Draw reflected rays at point A and C and mark them as AB and CD respectively. Extend them further. They do not meet on extension in the forward direction. Now extend them backwards. They meet at a point, mark this point as T. Point A is virtual image of object O. For our eyes placed at point E, these reflected rays appear to come from point I. Since the reflected rays do not meet at Abut only appear to do so, we can say that the image is virtual. Virtual image cannot be obtained on screen.
Question 2.
Differentiate between virtual and real images.
Answer:
S. No | Virtual Image | Real Image |
1 | A virtual image is formed when the rays of light after reflection or refraction appear to meet at a point. |
A real image is formed when the rays of light after reflection or refraction actually meet at some point |
2 | These images can not be seen on screen. | The image formed which can be taken on screen is called Real Image. |
Question 3.
Explain the regular and diffused reflection with the help of a diagram.
Answer:
Regular and Diffused 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 mirror or other smooth and bright surface.
Irregular 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 diffusion reflection. Diffusion reflection is caused by irregular surface of the reflector. Diffused reflection occurs on the irregular surface such as. book, surface of table, etc. The presence of light under a tree and inside the room is because of diffused reflection.
Activity Based Work
As shown in figure, make a simple periscope with two mirrors arranged in Z shaped box. Put its upper part towards the scene and view through the bottom. By this method you can easily see the scenes of upper parts while remaining at bottom position.
Hints : Students should themselves make a simple periscope as stated in the Activity based work
Activities
Activity 1: (Page 131)
Question 1.
Why is the spot of light formed on the wall of the building?
Answer:
When incident light falls on a plane mirror then the mirror changes the direction of the incident light that falls on the wall of the building.
Question 2.
What is known as reflection of light?
Answer:
The phenomenon of reflection of light- rays after colliding with a mirror or any other shiny object back into the same medium is called reflection of light.
Activity 2: (page 132)
Question 1.
Are the Incident angle and the Reflected angle same?
Answer:
Yes the Incident angle and the Reflected angles are same.
Question 2.
Write the first law of reflection.
Answer:
According to this law, the value of Incident angle and the Reflected angle are always same.
Incident angle (i) = Reflected angles (r)
Question 3.
Write the second law of reflection.
Answer:
According to the second law of reflection, incident ray, reflected ray and normal all exist in same plane.
Activity 3 : (Page 134)
Question 1.
How is the image seen? Erect or inverted?
Answer:
The image formed by a plane mirror is upright (erect).
Question 2.
When compared to the object of the image (pencil) is big or small?
Answer:
The image of the object is equal in size to the object.
Activity 4: (Page 135)
Question 1.
Observe the image and find out how far is it from the mirror?
Answer:
The distance of the image is equal to the distance of the object from the mirror.
Question 2.
Does the image of the object appears on the screen?
Answer:
No, the image cannot be seen on the screen.
Question 3.
How many types of images are there?
Answer:
There are two types of images-
- Virtual image and
- Real image.
Question 4.
What is a Virtual Image?
Answer:
The image which cannot be obtained on screen is called Virtual Image.
Question 5.
What is a Real Image?
Answer:
Image formed at any point which can be taken on screen is called Real Image.
Activity 5: (page 136)
Question 1.
What is the reflection of an object with a plane mirror?
Answer:
In the plane mirror the image is virtual.
Question 2.
Why the image from the plane mirror is called virtual?
Answer:
The image which cannot be obtained on screen is called Virtual image. These images seem to form at a point but practically no image is formed at that point.
Question 3.
Can the virtual image be found in the screen?
Answer:
No, the virtual image can not be found on the screen.
Activity 6: (Page 137)
Question 1.
How many images of pen are formed?
Answer:
Three images Question
Question 2.
Write the formula for calculating the number of images formed for an object placed between two parallel mirrors at a certain angle.
Answer:
The formula for calculating the number of images formed for an object placed between two plane mirrors at a certain angle is:-
Number of images (N) =
\(\left( \cfrac { { 360 }^{ \circ } }{ Angle\quad between\quad the\quad mirriors } \right) -1\)
Angle between the mirrors
Question 3.
On keeping the two mirrors parallel, how many reflections of the object in their middle are formed?
Answer:
If the angle between the two mirrors is zero i.e. both are parallel to each other then the number of images formed will be infinite.
Activity 7: (Page 138)
Question 1.
Can you see your image on the spoon?
Answer:
Yes, I can see my image on the spoon.
Question 2.
Is this image comparatively big or small?
Answer:
The image appears to be big.
Question 3.
Gradually take away the spoon from your face and observe the image. How is it transformed?
Answer:
Image appears to be small.
Question 4.
Revert the spoon and gradually take away the spoon from your face and observe the image ?
Answer:
The image appears to be upright from the reversed spoon.
Activity 8: (Page 139)
Question 1.
What are these spherical parts known as?
Answer:
These spherical parts are known as concave and convex parts.
Question 2.
What is a convex mirror?
Answer:
A spherical mirror in which the outwardly curved part works as reflector is called Convex Mirror.
Question 3.
What is concave mirror?
Answer:
A spherical mirror in which the bulged inward part i.e. the center of the spherical mirror work as reflector is called Concave mirror.
Activity 9: (Page 140)
Question 1.
Hold the mirror and the sheet for few minutes in the same position. What do you observe?
Answer:
We observe that, first the smoke appears and then the paper catches fire.
Question 2.
Why does the paper catches fire?
Answer:
The parallel rays coming from the sun are converged as a bright sharp spot by a concave mirror.This bright spot light on paper sheet is the image of the sun. Heat is generated by focusing sun light at a point due to which the paper catches fire.
Activity 10: (Page 141)
Question 1.
Can you see a bright sharp spot of light on the paper?
Answer:
No, we cannot get a bright sharp spot of light on the paper.
Question 2.
Why is the convex mirror called a Divergent mirror?
Answer:
The parallel rays coming from sun are not converged at spot by the convex mirror but spread (diverged). That is why the convex mirror is called a Divergent mirror.
Question 3.
What is known as Focus of convex mirror?
Answer:
Incident rays from a convex mirror parallel to principal axis seem to come from a point on principal axis after reflection. This point is called Focus of convex mirror.
Activity 11: (page 141)
Question 1.
What is the nature of the image usually obtained from a concave mirror?
Answer:
Real Image.
Question 2.
When does the virtual image is formed from a concave mirror?
Answer:
In the situation when the position of candle is in between F and mirror, you will not be able to get image.
Other Important Questions
Multiple Choice Questions
Question 1.
From which mirror can we make virtual image of any object bigger than the object.
(a) By Convex mirror
(b) By Concave mirror
(c) By plane mirror
(d) It is not possible.
Answer:
(b) By Concave mirror
Question 2.
Which mirror is used to make a smaller and virtual reflection of an object?
(a) By plane mirror
(b) By Concave mirror
(c) By Convex mirror
(d) By all these
Answer:
(c) By Convex mirror
Question 3.
What is the relation between focus length (f) and radius of curvature (R).
(a) Focus distance= Radius of curvature
(b) Focus Distance= 1/Radius of curvature
(c) 2 x Focus distance= Radius of curvature
(d) Focus distance= 2 x radius of curvature
Answer:
(c) 2 x Focus distance= Radius of curvature
Question 4.
The focus length of a plane mirror is?
(a) 0
(b) Infinite
(c) 25 cm
(d) -25 cm
Answer:
(b) Infinite
Question 5.
Where will be the reflection made of any object kept in front of the convex mirror?
(a) In place of the object
(b) At double the distance, from the place where object is kept in front of the mirror
(c) At half the distance, from the place where object is kept in front of the mirror
(d) At back of the mirror
Answer:
(d) At back of the mirror
Fill in the blanks
1. The phenomenon of reflection of light rays after colliding with a mirror or any other object back into same medium is called …………
2. The angle between incident ray and normal ray is called ………
3. Reflection caused by irregular surface is called ………. reflection
4. The image which can be obtained in screen is called……. image.
Answer:
- Reflection
- Angle of incidence
- Diffused
- Real
Very Short Answer Type Questions
Question 1.
What is the relation between angle of incidence and angle of reflection?
Answer:
Value of angle of incidence and angle of reflection is always equal.
Question 2.
What is the second law of reflection?
Answer:
The incident ray, reflected ray and normal, all lie in same plane.
Question 3.
What is the characteristic of image formed by plane mirror?
Answer:
Image formed by plane mirror is always erect and is equal to the size of object.
Question 4.
What is a virtual image?
Answer:
Image which cannot be obtained on screen is called Virtual image.
Question 5.
What is a real image?
Answer:
Image which can be obtained on screen is called real image.
Question 6.
How many types of spherical mirrors are there?
Answer:
There are 2 types of spherical mirrors.
- Concave Mirror
- Convex Mirror
Question 7.
Why is concave mirror known as converging mirror?
Answer:
Concave mirror converge all the light incident on it. Hence it is known as converging mirror.
Question 8.
Why is convex mirror known as diverging mirror?
Answer:
Because it diverges a beam of light falling on it.
Question 9.
Write the characteristic of image formed by a convex mirror?
Answer:
Image formed by a convex mirror is erect, virtual, smaller than the object and is formed behind the mirror.
Question 10.
What is the main use of a convex mirror?
Answer:
Convex mirror is usually used as rear view mirror (side glass) in vehicles.
Short Answers Type Questions
Question 1.
What are Good and moderate reflectors?
Answer:
Surfaces which reflect majority of the light falling on it are called good or best reflectors. For example, smooth and polished surface of an object, mirror etc. Other surfaces which reflect only a part of light are moderate reflectors.
Question 2.
Write the characteristic of image formed by a plane mirror?
Answer:
- Image formed by a plane mirror is always virtual and small.
- Size of the image is equal to the object.
- Reflection is made at a distance equal to the distance of the object placed in front of the mirror.
- Image is laterally transformed.
Question 3.
Explain spherical mirrors with diagrams.
Answer:
Concave Mirror- A spherical mirror in which the centre of the spherical mirror 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 4.
What is focus length of a mirror? What is the relation between focus distance and radius of curvature?
Ans.
Length from the spherical pole of the mirror to the main focus is called focus length. Focus length of a mirror is half the radius of curvature. Focus Length= Radius of curvature/2
Question 5.
What is called Image of an object? How many types of images are there?
Answer:
Image- When an object is kept in front of the mirror, shape of the object is made on the mirror. This shape is called the image of an object. When light travels from a point, after reflection,meet on a second point, i.e it appears to be coming from a second point. Second point is called image of the first point. There are 2 types of Images
- Real Image
- Virtual Image
Question 6.
Describe main focus or focus of spherical mirrors?
Ans.
Parallel to the main axis of spherical mirror, point where light meets (Concave mirror) or appears to be meet (Convex mirror) is called focus of spherical mirror. It is represented by letter F.
Question 7.
What is centre of curvature?
Answer:
Centre of the sphere of the circle, of which spherical mirror is a part, is called centre of curvature. In Concave mirror, it is situated at the reflector bottom, and in convex mirror, it is situated on other side of the reflector bottom. It is represented by letter C.
Question 8.
Which mirror is used for reflection in case of street lamps?
Answer:
Convex mirrors are used for reflection in street lamps. Because light of the lamp , after getting reflected from convex mirror , gets converted into a diverging beam, due to which light of the lamp gets spread on a wide area of the road.
Question 9.
What are the main uses of a concave mirror?
Answer:
Uses of a concave mirror:
- Generally concave mirror 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 shaving.
- 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 patient’s teeth.
Question 10.
What are the main uses of convex mirror?
Answer:
Uses of convex mirror:
Convex mirrors are mostly used as side glass of vehicles. These mirrors are clamped at the side of the vehicles and drivers can view the vehicles at its rear side so that he can drive safely.Primary importance of convex mirrors is due to its ability to form an erect image though the size of the image is small. Thus viewing area is much more as they are curved towards the outer side. Therefore, as compared to a plane mirror, convex mirrors provide a larger view to the driver.
Long Answer Type Questions
Question 1.
With the help of the diagram, explain below in reference to spherical mirrors:
1. Pole of mirror
2. Centre of curvature
3. Radius of curvature
4. Principal axis
5. Normal
6. Focus length
Answer:
- Pole of Mirror : The middle point of the reflecting surface is known as the pole of the mirror. It is situated on the face of the mirror and it is represented by P.
- Centre of curvature : The centre of the spherical mirror, which is a portion of mirror is called centre of curvature. It is represented by C.
- Radius of curvature: The reflecting surface of a spherical mirror which is a portion of sphere has radius R which is called radius of curvature. It is represented by R.
- Principal axis: The line joining the pole and centre of curvature of the mirror is called Principal axis.
- Normal: Line joining pole of the spherical mirrors and centre of curvature is perpendicular on it. Therefore any perpendicular line of the spherical mirrors is equal to its centre of curvature.
- Focus Length : Length of the pole of the spherical mirror to the main focus is known as Focus length. It is represented by f.
Question 2.
Explain images formed by convex mirrors with the help of diagram.
Answer:
For every case of convex mirror, image of an object formed is virtual, erect, smaller than the object, at the back of the mirror and at the middle focus.Suppose there is an object named 00’. After reflection, the ray of light parallel to principal axis passes through focus. Another ray O’ B which appears to pass from centre of curvature C, gets reflected back in same path. Both these reflected rays appear to come from point I, which is the image of object 00. Image is formed between focus and pole which is virtual, erect and smaller than object.
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