Question

An astronomical telescope has two lenses of focal powers $0.5\, D$ and $20\, D$. Then its magnifying power will be :

• A. 8
• B. 20
• C. 30
• D. 40

Answer 1

Answer: (D)

40

Answer 2

Here $:$ Focal power of first lens $P_{1}=0.5\, D$ Focal power of second lens $P_{2}=20\, D$ Using the relation for magnifying power $m=\frac{f_{o}}{f_{e}}=\frac{P_{2}}{P_{1}}=\frac{20}{0.5}=40$