Question

find the distance at which an object should be placed in front of a convex lens of focal length 20m to obtain a virtual image of thrice it's size​

Answer 1

Answer:

Step-by-step explanation:

All Real, so all Positive. Also v=2u

1/u + 1/v = 1/f

1/u + 1/2u = 1/20

3/2u = 1/20

2u/3 = 20

u=30 (and v=60)