Question

A mirror of focal length 15 cm forms an erect image, 3 times the size of the object. The distance between the object and mirror is:
5cm

30cm

15cm

10cm

Answer 1

Answer:

Focal length(f)= -15 cm, magnification= -3 (image is real). So, -v/u=-3 ; or v=3u {v=image distance and u=object distance}. Using mirror formula,

1/f= 1/v + 1/u

-1/15 = 1/3u + 1/u

4/3u = -1/15

u= -20 cm

v =3u= 3×(-20)= -60 cm

So object is 20 cm and image is 60 cm in front of the mirror.