Question

Why is the power of a lens is measured as reciprocal of focal length? Give reason.

Answer 1

as we know that the power of a lens is defined as the ability of lens to converge or diverge incoming light rays

Answer 2

$Power = \frac {1}{Focal Length}$ is the Relation

Explanation:

• We know from the definition, power of a lens is defined as the ability of a lens to converge or diverge incoming light rays.
• So, a lens of a higher power would converge or diverge light rays to a greater extent.
• Now, the focal length of a lens is also related to its diverging or converging ability but it varies inversely.
• Thus, the relation between power and focal length is inverse such that power is given as the reciprocal of the focal length of a lens.
• F = $\frac {1}{T}$