Light (NCERT Solutions, Class 7)

(1) Fill in the blanks:

(a) An image that cannot be obtained on a screen is called_____.

(b) Image formed by a convex ____is always virtual and smaller in size.

(c) An image formed by a ____mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called ____image.

(e) An image formed by a concave ____ can not be obtained on a screen.

Ans-

(a) An image that cannot be obtained on a screen is called virtual image.

(b) Image formed by a convex mirror is always virtual and smaller in size.

(c) An image formed by a plane mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called real image.

(e) An image formed by a concave lens can not be obtained on a screen.

(2) Mark ‘T’ if the statement is true and “F” if it is false:

(a) We can obtain an enlarged and erect image by a convex mirror.

(b) A concave lens always from a virtual image.

(c) We can obtain a real, enlarged and inverted image by a concave mirror.

(d) A real image can not be obtained on a screen.

(e ) A Concave mirror always form a real image.

Ans-

(a) We can obtain an enlarged and erect image by a convex mirror. F

(b) A concave lens always from a virtual image. T

(c) We can obtain a real, enlarged and inverted image by a concave mirror. T

(d) A real image can not be obtained on a screen. F

(e ) A Concave mirror always form a real image. F

(3) Match the items given in Column I with one or more items of Column II.

Column I                                            Column II

(a) A plane mirror                             (i)Used as a magnifying glass.

(b) A convex mirror                          (ii) Can form image of objects spread over a

large area.

(c) A convex lens                               (iii) Used by dentists to see enlarged image of

teeth.

(d) A concave mirror                        (iv) The image is always inverted and magnified.

(e) A concave lens                            (v) The image is erect and of the same size as

the object.

(vi) The image is erect and smaller in size than

the object.

Ans-

Column I Ans Column II
(a) A plane mirror (c) (i)Used as a magnifying glass.
(b) A convex mirror (b) (ii) Can form image of objects spread over a                                                                large area.

 

(c) A convex lens (d) (iii) Used by dentists to see enlarged image of                                                                 teeth.

 

(d) A concave mirror (c) (iv) The image is always inverted and magnified.
(e) A concave lens (a) (v) The image is erect and of the same size as                                                                    the object.

 

(e)                                                             (vi) The image is erect and smaller in size than                                                                 the object.

 

(4) State the characteristics of the image formed by a plane mirror.

Ans- Characteristics of the image formed by a plane mirror are given below-

(i) Virtual image is formed by plane mirror.

(ii) Image is of the same size as the object.

(iii)Image formed by the plane mirror is erect.

(iv) Image is at the same distance behind the mirror as the object is in front of it.

(v)In an image formed by a mirror, the left side of the object is seen on the right side in the image and vice- versa.

(5) Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

Ans-Letters A, H, I, M, O, T, U, V, W, X, Y formed exactly same image when keep in front of the plane mirror. These letters have vertical symmetry. So, they look same even when their sides interchanged.

(6) What is a virtual image? Give one situation where a virtual image is formed.

Ans- The image which could not be formed on screen is called virtual image. This could be obtained by plane mirror.

Eg:-  Image of flower in the plane mirror is an example of virtual image.

(7) State two differences between a convex and a concave lens.

Ans- Two differences between concave and convex lens are given below-

SN Concave lens Convex lens
1. These are thinner in the middle. Thicker in the middle.
2. Divergent lens Convergent lens.

 (8) Give one use each of a concave and a convex mirror.

Ans-

SN Convex mirror Concave mirror
1. Used in side view mirror Used in makeup and shaving.

(9) Which type of mirror can form a real image?

Ans- Concave mirror can formed real image.

(10) Which type of lens forms always a virtual image?

Ans- A concave lens always forms a virtual image.

Choose the correct option in question 11-13

(11) A virtual image larger than the object can be produced by a

(i)concave lens

(ii) concave mirror

(iii) convex mirror

(iv) plane mirror

Ans-

(ii) concave mirror   

(12) David Is observing his image in a plane mirror. The distance between the mirror and his image is 4 cm. If he moves 1m towards the mirror, then the distance between David and his image will be

(i) 3m

(ii) 5m

(iii) 6m

(iv) 8m

Ans(iii) 6m

Distance between the David and his image

= Distance between the mirror and David + Distance between mirror and image

Distance between mirror and image =4 – 1

=3m (he moved 1m towards the mirror)

Distance between the mirror and David=3m

Distance between the David and his image = 3 +3=6m

(13) The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be

(i) 1m/s

(ii) 2m/s

(iii) 4m/s

(iv) 8m/s

Ans-(iii) 4m/s   √

The image of truck approach to the driver at double the speed of car because distance between the car and truck’s image is decreasing at double rate.

Helping Topics

Light

Practice sheet, class 7

Picture1

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