Question

A convex lens of focal length $1.0cm$ and a concave lens of focal length $0.25m$ are $0.75m$ apart. A parallel beam of light is incident on the convex lens. The beam emerging after refracting from both lenses is

• A. Parallel to the principal axis
• B. Convergent
• C. Divergent
• D. None of the above

Answer 1

Answer: (A)

Parallel to the principal axis

Power of system

$\frac{1}{f_1}+\frac{1}{f_2}-\frac{d}{f_1{f}_2}=\frac{1}{1}+\frac{1}{-0.25}-\frac{0.75}{\left(1\right)(-0.25)}$

$=1-4+3=-3+3=0$

Since power of the system is zero, therefore the incident parallel beam of light will remain parallel after emerging from the system.