JAMB - Physics (1998 - No. 31)
A man wears convex lens glasses of focal length 30cm in order to correct his eye defect. instead of the optimum 25cm, his least distance of distinct vision is
14cm
28cm
75cm
150cm
Explication
F = \(\frac{uv}{u + v}\)
F = +ve
v = -ve
30 = \(\frac {25 {\times} (-v)}{25 + (-v)}\)
-25v = 750 - 30v
5v = 750
v = 150cm
(Note that either negative or positive values go to show the positioning and hence, they are not a strong necessity in your final answer.)