Question

A 10cm long stick is kept in front of a concave mirror having focal length of 10cm in a such way that the end of the stick closest to the pole is at a distance of 20cm. What will be the length of the image?

Answer 1

Given that,

For concave mirror 

For end A:

Focal length f= -10cm

Object distance u = -30cm

We know that, the mirrors formula is given by,

1/f= 1/u + 1/v

1/-10= 1/-30 + 1/v

Thus, 1/v = -1/10 + 1/30

Hence, 1/v = -2/30

v = -15 cm

 

For end B:

Focal length f= -10cm

Object distance u= -20cm

We know that the mirrors formula is given by,

1/f = 1/u + 1/v

1/-10= 1/-20 + 1/v

Thus, 1/v = -1/10 + 1/20

Hence, v= -20cm

 

Thus, the length of the image formed is given by,

20 – 15= 5 cm