The power of a convex lens of focal length 25 cm is ______________.
A
$4.0 D$
B
$0.25 D$
C
$-4.0 D$
D
$-0.4 D$
Answer
$4.0 D$ $\begin{aligned} \text { Hint: Power of lens } & =\frac{1}{\text { focal length in metre }} \\ & =\frac{1}{0.25}=4.0 D \end{aligned}$ As, focal length of convex lens is always positive, power of convex lens is also positive.