A converging beam of rays is incident on a diverging lens. Having passed through the lens the rays intersect at a point 15cm from the lens on the opposite side. If the lens is removed the point where the rays meets will move 5cm closer to the lens. The focal length of the lens is
5cm
cm
20cm
cm
Solution:
1/v - 1/u = 1/f u = 10 v = 15 f = ? 1/15 - 1/10 = 1/f ∴f = -30cm