A normal eye has its retina positioned 2 cm behind the eye-lens. Determine the power of the eye-lens when the eye is fully relaxed.

Step-by-step solution

When the eye is fully relaxed, it focuses parallel rays from an object at infinity onto the retina. Object distance, u = - Image distance, v = 2 cm = 0.02 m Using the lens formula: 1 f = 1 v - 1 u 1 f = 1 0.02 - 1 - 1 f = 50 m ⁻¹ The power of the eye-lens is given by: P = 1 f = 50 D