Question

power of a lens is -4 its focal length is what

Answer 1

power of a lens is -4 its focal length is -0.25

Answer 2

Answer:

Power of a lens is -4 means its a concave lens of focal length -25 cm.

Explanation:

Since the degree of light beam convergence or divergence depends on the focal length of the lens, the power of the lens can be defined as the reciprocal of the focal length of the lens. For example, if the focal length (f) of the lens is 1 m, the refractive power (p) of the lens is 1 / f = 1/1 = 1 dioptre.

$Given:\\POWER =P= -4D\\ P = \frac{1}{F}\\F= focal length of lens$

$F in (cm) = 100/P$

$= 100/-4 \\\\ = -25 cm.$

• A negative focal length means that the lens diverges light.
• Power of a lens is -4 means its a concave lens of focal length -25 cm.