A student-focused the image of a candle flame on a screen using a convex lens. He noted down the positions of the candle, screen, and lens on the scale as under :
Position of candle = 10.0 cm
Position of lens = 50.0 cm
Position of screen = 90.0 cm
The power of the lens is
1
2.5 D
2
5.0 D
3
10.0 D
4
20.0 D