If a concave lens of focal length 12cm is used to produce a real image four times the size of the object, how far from the lens must the object be placed?
- 10 cm
-
15 cm
- 20 cm
- 25 cm
The correct answer is: B
Explanation
Magnifications = V/U = 4
∴ V = 4U
1/V + 1/U = 1/f
1/4u + 1/U = 1/12
5/4U = 1/12
4U = 12 x 5 = 60
∴ U = 15 cm
There is an explanation video available .