A farsighted person is unable to see objects placed closer than 50 cm . Determine the power of the lens required to see objects located at 20 cm .

Step-by-step solution

For a farsighted person, the lens must form a virtual image of the object at the person's near point. Given object distance, u = -20 cm Image distance, v = -50 cm Using the lens formula: 1 f = 1 v - 1 u 1 f = 1 -50 - 1 -20 1 f = - 1 50 + 1 20 1 f = -2 + 5 100 = 3 100 cm ⁻¹ The focal length of the lens is f = 100 3 cm = 1 3 m The power of the lens is given by P = 1 f( in m ) P = +3 D