Question

The far point of a myopic person is $100\text{cm}$ in front of the eye. What is the nature and power of the lens required to correct the problem?

• A. Convex lens, Power = $+1.5\text{D}$
• B. Concave lens, Power = $-1.5\text{D}$
• C. Convex lens, Power = $+1\text{D}$
• D. Concave lens, Power = $-1\text{D}$

Answer 1

The correct option is D Concave lens, Power = $-1\text{D}$

A myopic person can see things nearby clearly but cannot see things far. We need a lens that forms an image at $100\text{cm}$ for an object at infinity.

Using lens formula $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$
$u=-\infty$
$v=-100\text{cm}$
$\frac{1}{f}=-\frac{1}{100}\text{cm}$
$\text{Power = - 100 cm = - 1 D}$
Negative focal length is a concave lens.