Question

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

• A. - 1.5 D
• B. -6.5 D
• C. + 6.5 D
• D. + 6.67 D

Answer 1

Answer: (A)

- 1.5 D

Answer 2

$P=P_1+P_2=\frac{1}{f_1(m)}+\frac{1}{f_2(m)}=\frac{1}{0.4}-\frac{1}{0.25}=-1.5 D$