Question

For a combination of two convex lenses of focal lengths \( f_1 \) and \( f_2 \) to act as a glass slab, the distance of separation between them is:

• A. \( f_1 + f_2 \)
• B. \( f_1 - f_2 \)
• C. \( \frac{f_1 + f_2}{2} \)
• D. \( \frac{f_1 - f_2}{2} \)

Hint:

When two convex lenses act as a glass slab, the optical path remains unchanged, requiring a separation of \( f_1 + f_2 \).

Answer 1

The Correct Option is A

For two convex lenses to act as a glass slab, the net optical path difference should be zero. This happens when the separation between the lenses is equal to the sum of their focal lengths: \[ d = f_1 + f_2 \]