Question

find the power and the nature of a lens with focal length of - 20 CM​

Answer 1

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=

f(inmetres)

1

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

(−0.2)

1

= > power = - 5 \: D=>power=−5D

So final answer :

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

power=−5D