Question

A convex lens of focal length 0.5 m and concave lens of focal length 1 m are combined. The power of the resulting lens will be:

• A. - 1 D
• B. 0.5 D
• C. 1D
• D. - 0.5 D

Answer 1

Answer: (C)

1D

Answer 2

From the relation $\frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}$ $=\frac{1}{0.5}+\frac{1}{-1.0}=2-1=1\,D$