Question

How far from a concave mirror of focal length 0.5m must a linear object be placed to give an image four times as long as the object ?

Answer 1

Given :

A concave mirror of focal length

0.5 m

To Find :

Distance where linear object be placed to give an image four times as long as the object.

Solution :

•Given a concave mirror of focal length 0.5 m

& length of image produced is four times the length of image .

i.e. m = 4

-v/u = 4

v = -4u

•where v is position of image from mirror & u os position of object from mirror

•Now , By mirror formula

1/v + 1/u = 1/f

putting v = -4u

-1/4u + 1/u = 1/0.5

(-1+4)/4u = 2

-3/4u = 2

u = -3/8 = -37.5 cm

•Hence , object should be placed 37.5 cm in front of mirror

Answer 2

Answer:

u=-37.5cm

Explanation:

m=4

-v/u=4u

v=-4u

1/v+1/u=1/0.05

(-1+4)/4u =2

-3/4u=2

u=-3/8

u=-37.5