Question

The focal length of a lens is -150 cm. Find the power of the lens and what lens is it ?​

Answer 1

Explanation:

power of lens = 1/ focal length (in meter)

= 1/ - 150 cm

= - 100/ 150 m

. = -2/3 m

= -0.67 diopter

lens = concave lens

Answer 2

Given :

Focal length : -150 cm.

To find :

The power of the lens.

Solution :

The focal length is negative soo it is concave lens.

We know that,

The power of a lens is inversely proportional to its focal length so, a lens of short focal length has more power whereas a lens of long length has less power.

The unit of power of a lens is dioptre.

» The power is the reciprocal of the focal length that is

$\boxed{ \bf P = \dfrac{1}{f} }$

where,

• P denotes power of the lens
• f denotes the focal length

By, substituting the given values in the formula,

$\dashrightarrow\sf P = \dfrac{1}{f}$

$\dashrightarrow\sf P = \dfrac{1}{ - 150} × 100 \: ( in \: metres)$

$\dashrightarrow\sf P = - 0.67 \: D$

Thus, the power of the lens is -0.67D