Question

A symmetrical biconvex lens of focal length ‘f’ is cut into four identical pieces along its principal axis and perpendicular to the principal axis. The focal length of one of the four pieces is

• A. $\frac{f}{4}$
• B. $\frac{f}{2}$
• C. 2 f
• D. 4 f

Answer 1

Answer: (C)

2 f

For this we first cut lens along its principal axis in two equal parts. In this case focal length remains same. hence now focal length of each part is $f$.

After that we cut the each part perpendicular to the lens. In this case focal length of each part becomes double of the original length. which is $2f$.

Hence we get four equal parts of focal length $2f$ each part.