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
-
A.
14cm -
B.
28cm -
C.
75cm -
D.
150cm
Correct Answer: Option A
Explanation
F = (frac{uv}{u – v})
F = +ve
v = -ve
30 = (frac {25 {times} (-v)}{25 – (-v)})
v = (frac {25 {times} (-v)}{25+v})
v = 14cm
(Note that either negative or positive values go to show the positioning and hence, they are not a strong necessity in your final answer.)