CBSE · Class 10 · Science · The Human Eye and Colourful WorldA person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of corrective lens used to restore proper vision? Also, calculate the power of the lens required.

To correct myopia (near-sightedness), a concave lens is used.

Given:

• Far point of the myopic person ($v$) = $-1.2$ m
• Object distance ($u$) = $-\infty$ \nUsing the lens formula: $$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$$ \nSubstitute the values: $$\frac{1}{f} = \frac{1}{-1.2} - \frac{1}{-\infty}$| $$\frac{1}{f} = \frac{1}{-1.2} - 0$$ $$f = -1.2\text{ m}$$ \nNow, calculating the power of the lens ($P$): $$P = \frac{1}{f \text{ (in metres)}}$$ $$P = \frac{1}{-1.2} \text{ D}$$ $$P = -0.83\text{ D}$| \nTherefore, a concave lens of power $-0.83$ D is required to correct the defect.