JAMB - Physics (1990 - No. 22)
What must be the distance between an object and a converging lens of focal length 20cm to produce an erect image two times the object height?
20cm
15cm
10cm
5cm
解释
F = \(\frac{uv}{u + v}\); v = 2u
20 = \(\frac{ux - 2u}{u + (-2u)}\); u = 10cm
20 = \(\frac{ux - 2u}{u + (-2u)}\); u = 10cm