Question

An object is placed at 30cm in front of the concave mirror, image is
also formed at 30cm in front of the mirror. Then the focal length is
a. 30cm
b. 15cm
c. 20cm
d. infinity

Answer 1

Answer:

Here,

u= -30 cm

f= -20 cm

By using mirror formula,

1/v + 1/u = 1/f

1/v + 1/-30 = 1/-20

v= -60 cm

negative sign indicates that image is in front of the mirror

Therefore,

The distance between image and object = 60-30=30cm