Question

A person is advised to use a lens of power +2 D for correcting his vision. Identify the defect of vision, and find the focal length of the lens.

• A. Hypermetropia, 0.5 m
• B. Hypermetropia, -0.5 m
• C. Myopia, 0.5 m
• D. Myopia, -0.5 m

Answer 1

The correct option is A Hypermetropia, 0.5 m

Power, P = $\frac{1}{f\left(inm\right)}$

The power and focal length of a convex lens are positive and those of a concave lens are negative. Here, the power of the lens is +2 D. So, it is a convex lens.

A convex lens is used to rectify hypermetropia. Therefore, the defect with which the person is suffering from is hypermetropia.

The power of the lens is:

P = $\frac{1}{f}$

f = $\frac{1}{P}$

= $\frac{1}{2}$

= 0.5 m