Question 9.
Solve the following examples.
The doctor has prescribed a lens having power +1.5 D. What will be the focal length of the lens? What is the type of the lens and what must be the defect of vision?
Answer:
Power of lens is defined as the reciprocal of its focal length so
1.5 = 1/f
1.5f = 1
⇒ f = 1/1.5
⇒ f= 0.67m
As the focal length is positive so the lens prescribed is positive and has positive power. It is a convex lens. The defect of the vision is Hypermetropia.
