Question

A lens of power $+2.0\text{D}$ is placed in contact with another of power $-1.0\text{D}$. The combination will behave like

• A. A converging lens of focal length $100\text{cm}$
• B. A diverging lens of focal length $100\text{cm}$
• C. A converging lens of focal length $50\text{cm}$
• D. A diverging lens of focal length $50\text{cm}$

Answer 1

The correct option is A A converging lens of focal length $100\text{cm}$

Given $P_1=2\text{D},P_2=-1\text{D}$
Power of combination is
$P=P_1+P_2=1\text{D}$
Using the formula, $P=\frac{1}{f\left(inm\right)}$
$1=\frac{1}{f\left(inm\right)}$
$f=1\text{m}$
$f^{}=100\text{cm}$