Question

How does the power of a lens change if its focal length is doubled?

• A. Power gets halved
• B. Power gets doubled
• C. Power does not changed
• D. Power increases

Answer 1

The correct option is A Power gets halved

$P=\frac{1}{f}$
Thus, when $f$ becomes $2f$, $P^{\prime }=\frac{1}{2f}=\frac{P}{2}$ i.e. power is halved.