Question

A person uses a convex lens of focal length 20 cm in spectacles , the power of lens will be​

Answer 1

Answer:

+5 D

Explanation:

As we know that, the formula to calculate the power of a lens is 1/f = P.

Here f should be converted into meters first so, 20 cm is 0.2 meters.

using power formula,

1/0.2 = 5

As it is a convex lens so the power will be in positive.

Hence, the power is +5D

Answer 2

The convex lens will have a 5 dioptre power.

Explanation:

• A convex lens converges light beams that travel parallel to its primary axis, which is comparatively thick in the center and thin at the lower and higher ends. Instead of curving inside, the edges curve outward.

Here, the focal length is 20 cm and we need to find the power of the convex lens.

So, Power$=\frac{1}{f}\times100$

∴ $\frac{1}{20}\times100$

⇒ $5D$

As a result, the lens has a 5 dioptre power.