A person has a near point at 100 cm . What power of lens is required to read at 20 cm if they use a contact lens?

Step-by-step solution

The person wants to read at a distance of 20 cm . Therefore, the object distance is u = -20 cm = -0.2 m . The near point of the person is 100 cm . The lens must form the image of the object at this near point. Therefore, the image distance is v = -100 cm = -1 m . Using the lens formula, the power P of the lens is given by: P = 1 f = 1 v - 1 u Substituting the values of v and u : P = 1 -1 - 1 -0.2 P = -1 + 5 = +4 D