Question

State the condition for the following:

A lens has both its focal lengths equal.

• A. Medium is different on either side of lens.
• B. Medium is same on either side of lens.
• C. No condition required
• D. Can't say

Answer 1

The correct option is B Medium is same on either side of lens.

Focal length is the distance between focal point and center of lens. Focal point is the point where parallel rays meet after passing through the lens. If the medium on both sides is same, the focal point will be the same and hence, same focal lengths.