A lens of focal length 15cm forms an erect image which is...
A lens of focal length 15cm forms an erect image which is three times the size of the object. The distance between the object and the image is ___
10cm
20cm
30cm
40cm
Correct answer is D
F= 15cm
M = 3
M = vu
V =3u
1f = 1u + 1v
115 = 1u - 13u
115 = 23u
U =10cm
D = u + v
= 10 +30 = 40cm