Question

A lens of power $+2$ dioptres is placed in contact with a lens of power $-1$ dioptre. The combination will behave like

• A. A convergent lens of focal length 50 cm
• B. A divergent lens of focal length 100 cm
• C. A convergent lens of focal length 100 cm
• D. A convergent lens of focal length 200 cm

Answer 1

Answer: (C)

$\frac{1}{f}-\frac{1}{f_1}+\frac{1}{f_2}=\frac{P_1}{100}+\frac{P_2}{100}=\frac{1}{100}\Rightarrow f=100cm$
$\therefore$ A convergent lens of focal length $100cm$.