Question

A thin convex lens is cut into two parts in different ways that are arranged in four manners as shown. Which arrangement will give maximum optical power ?

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Let the focal length and power of original convex lens be $f$ and $P$

If the lens is divided parallel to principal axis, both parts have the same focal length as original lens $\left(f\right)$ & if lens is cut perpendicular to principal axis, focal length of each part is $2f$.

Arrangement in option (b) and (d) will be having same power as for original lens.

For option (a), since the focal length of both the parts remains same, therefore total power $P=P_1+P_2=2P$

For option (c), since the focal length of both the parts becomes $2f$, therefore total power $P=P_1+P_2=\frac{P}{2}$

Therefore arrangement of parts in option (a) will have maximum power.

Hence, correct option is $\left(a\right)$.