The focal length of a convex lens is 25 cm. Express its power with sign.

As we know,

$\text{Power} = \dfrac{1}{\text{focal length}}$

Given,

focal length = 25 cm = 0.25m

Substituting the value of focal length in formula we get,

$\text{Power} = \dfrac{1}{\text{0.25 m}} \\[0.5em] \Rightarrow \text{Power} = 4 D \\[0.5em]$

As the lens used is convex in nature so power is positive.

Hence, P = +4D