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NCERT Solutions for class 7 Science chapter 15 – Light

Back Exercise

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 a _________ image.

(e) An image formed by a concave ___________ cannot be obtained on a screen.

Solution:

(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 a real image.

(e) An image formed by a concave lens cannot 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. (T/F)

(b) A concave lens always form a virtual image. (T/F)

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

(d) A real image cannot be obtained on a screen. (T/F)

(e) A concave mirror always form a real image. (T/F)

Solution:

a) False

b) True

c) True

d) False

e) False

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

Solution:

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

Solution:

Characteristics of the image formed by a plane mirror are as follows:

• Image distance and object distance are equal
• Size of object and image are equal
• The image formed is erect and virtual
• Images are laterally inverted

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.

Solution:

A, H, I, M, O, T, U, V, W, X, Y alphabets form images in a plane mirror exactly like the letter itself because these alphabets are laterally symmetric.

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

Solution:

The image that cannot be obtained on a screen is called a virtual image. The image formed by a plane mirror is virtual.

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

Solution:

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

Solution:

Concave mirrors are used in the headlights of cars and scooters.

Convex mirrors are used as side-view mirrors in vehicles.

9. Which type of mirror can form a real image?

Solution:

The concave mirror can form a real image.

10. Which type of lens forms always a virtual image?

Solution:

Concave lens form a virtual image.

Choose the correct option in questions 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

Solution:

The answer is (ii) concave mirror

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

(i) 3 m (ii) 5 m

(iii) 6 m (iv) 8 m

Solution:

The answer is (iii) 6 m

13. The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/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) 1 m/s (ii) 2 m/s

(iii) 4 m/s (iv) 8 m/s

Solution:

The answer is (iii) 4 m/s