Question

3. i) Give two uses each of a concave and a convex mirror.

ii) The rear view mirror of a car is a plane mirror. A driver is reversing his car

at a speed of 4 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​

Answer 1

Answer:

1. Solution:

Uses of Concave and Convex mirror are following:-

Concave mirror is used by dentist, solar furnace, reflector of a torch, etc.

ii.Convex mirror is used in rear view mirrors.

Correct option is (ii) 2m/s.

As the car moves 2m backward, the mirror also moves 2m backward, so the image comes 2m forward.

Answer 2

Answer:

i) . Concave mirrors can form enlarged image of the object. Therefore, they are used by the dentist to see the enlarged image of the patient’s teeth.

. Convex mirror forms diminished and upright image of the object. It is used as a side view mirror of the car because it enables the driver to view objects spread over a large area behind him/her.

ii)

(iii) 8 m/s

The speed of the car is 2 m/s which means the car is approaching the truck with a speed of 2 m per second. The distance between the car and truck will decrease at a double rate. This is because the image of the truck will travel a distance twice the distance travelled by the car in equal time. Hence, the image of the truck will appear to approach the driver with the speed of 4+4 = 8 m/s.