Question
A person with a myopic eye cannot see objects beyond $1.2 \ m$ distinctly. What should be the type of the corrective lens used to restore proper vision?
✓
Answer
- A person with a myopic eye should use a concave lens of suitable focal length or power to restore proper vision.
- [Here, the person with defect of myopia has the far point nearer than infinity at a distance of $1.2 \ m$ from the eye.
- So, $v=-1.2 m ; u =-\infty ; f =$ ?
- So, from the lens formula
- $\frac{1}{f}=\frac{1}{-u}-\frac{1}{v}$
- $\therefore \frac{1}{f}=\frac{1}{(-\infty)}+\frac{1}{-1.2}$
- $\therefore f=-1.2 m$
- $\therefore P=\frac{1}{-1.2}=-0.83 D$
- A concave lens of focal length $1.2 \ m$ should be used to restore proper vision.]
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