The focal length of a convex lens is 25 cm. Express its power with sign.
As we know,
Power=1focal length\text{Power} = \dfrac{1}{\text{focal length}}Power=focal length1
Given,
focal length = 25 cm = 0.25m
Substituting the value of focal length in formula we get,
Power=10.25 m⇒Power=4D\text{Power} = \dfrac{1}{\text{0.25 m}} \\[0.5em] \Rightarrow \text{Power} = 4 D \\[0.5em]Power=0.25 m1⇒Power=4D
As the lens used is convex in nature so power is positive.
Hence, P = +4D
