## Wednesday, 8 June 2016

### TEXTBOOK ANSWERS AND SOLUTIONS OF CBSE CLASS VII SCIENCE Chapter 15 Light

1)Fill in the blanks
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)

(a) F
(b) T
(c) T
(d) F
(e) F

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

(a) A plane mirror-      (v) The image is erect and of the same size as the object.
(b) A convex mirror-   (ii) Can form image of objects spread over a large area.
(c) A convex lens-       (i) Used as a magnifying glass.
(d) A concave mirror- (iii) Used by dentists to see enlarged image of teeth.
(e) A concave lens-     (vi) The image is erect and smaller in size than the object.

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

ANSWER:- Characteristics of the image formed by a plane mirror:
(i) The image formed is virtual
(ii) The image is laterally inverted.
(iii) It is of the same size as the object.
(iv) The image is situated at the same distance from the mirror as the object.
(v) The image is erected.

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

ANSWER:- The image which cannot be formed or obtained on the screen is called virtual image.
When we stand in front of our dressing table mirror, we use to see our virtual image. The virtual image is formed in case of plane and convex mirror.

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

Convex lens: -                         (i) Convex lens converges the light falling on it
(ii) Convex lens is thicker in the middle.

Concave lens:-                         i) Concave lens diverges the light falling on it

(ii) Concave lens is thinner in the middle.

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

ANSWER:- Concave mirror forms large images therefore it is used by dentists to see enlarged image of teeth. Convex mirror forms diminished image therefore it used as rear view mirror in vehicles.

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

ANSWER:- Concave mirror can form a real image.

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

ANSWER:- Concave lens forms always 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