Question

. An object of height 1.5 cm is placed at a distance of 20 cm from a concave mirror of focal length 15 cm. At what
distance from the mirror should a screen be placed so as to get a sharp image. Where should the screen be
moved if the object is moved towards the focus?

Answer 1

Answer:

h=2cm

u=-30cm(sign convention)

f=-15(sign convention)

v=?

1/f=1/v+1/u

1/-15=1/v+1/-30

1/-15-1/-30=1/v

2-1/-30=1/v

1/-30=1/v

v=-30cm

the screen should be placed 30cm in front of the mirror to obtain a sharp image

Answer 2

Given :

Height of the object = 1.5cm

Distance of the object from the mirror = 20cm

Focal length of the concave mirror = 15cm

To Find :

Distance of image From the mirror

Solution :

• For a concave mirror

           $\frac{1}{f} =\frac{1}{u} +\frac{1}{v}$

• By substituting the values in the above equation

          $\frac{1}{-15} =\frac{1}{-30} +\frac{1}{v}$

           $\frac{1}{v} =\frac{1}{-15} +\frac{1}{30}$

           $\frac{1}{v} =\frac{-1}{30}$

           $v=-30cm$

The screen should be placed at a dustane of 30cm infront of the mirror.