Question

Find the power and nature of a lens with focal length of - 20 cm.​

Answer 1

Answer:

power is -5D and nature of lens is concave

Explanation:

we know that power is reciprocal for focal length and negative sign indicates that is concave

Answer 2

Answer:

Given:

Focal length of lens = -20 cm

To find:

Power and nature of the given lens

Concept:

Focal length refers to the length of a point from the principle axis where Parallel rays of light meet after Refraction through the lens

Power of a lens is the index representing the diverging or converging power of a lens.

Calculation:

Focal length is -20 cm. Since it is negative in value , we can say that it is Diverging in nature (i.e It's Concave Lens)

Power is the reciprocal of focal length (in metres)

$\boxed{power = \dfrac{1}{f(in \: metres)} }$

$= > power = \dfrac{1}{( - 0.2)}$

$= > power = - 5 \: D$

So final answer :

$\boxed{ \red{ \huge{ \bold{ \sf{ \underline{ power = - 5 \: D }}}}}}$