Question

what is the focal length of a lens if it has power P=4D​

Answer 1

Answer:

Given Focal length (f) = 4D P (in diopter) =  1 f ( i n m e t e r s ) 1f(inmeters)  ⇒ 4 =  1 f ( i n m e t e r s ) 1f(inmeters) ⇒ f (in meters) =  1 4 14= 0.25m Now 1m = 100cm  ⇒ 0.25m = 25cm  Hence the focal length of lens is 25cmRead more on Sarthaks.com - https://www.sarthaks.com/951079/a-lens-has-power-4-d-find-the-focal-length-that-lens

Answer 2

$\huge \underline{ \mid \boxed{ \red{\mathfrak{ \: \: formula \: \: } } } \mid}$

$\boxed{ \pink{\sf focal \: \: \: length \: \: = \frac{1}{ \: \: power \: \: \: \: of \: \: \: lens \: \: } }}$

so ,

$\sf focal \: \: \: length \: (f) = \frac{1}{4} m = 0.25 \: m = 25cm$