Question

# A person with a myopic eye cannot see objects beyond $1.2\mathrm{m}$ distinctly. What should be the type of corrective lens used to restore proper vision?

Open in App
Solution

## Step 1. Formula to find the power of lensIn a normal eye, the distant point is infinity. The lens used should be such that an object at infinity, forms a virtual image at $1.2\mathrm{m}$.Formula to find the power of lens is, $\mathrm{P}=\frac{1}{\mathrm{f}}$Here, $\mathrm{P}$ is the power of the lens and $\mathrm{f}$ is the focal length.We know that the relation, $\frac{1}{\mathrm{f}}=\frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}}$Here, $\mathrm{v}$ is the image distance and $\mathrm{u}$ is the object distance.Step 2. Calculate the power of the corrective lens used to restore proper vision.It is given that, a person can't see objects beyond $1.2\mathrm{m}$ directly.So, in order to view the distances beyond $1.2\mathrm{m}$, from the given, $\mathrm{v}=-1.2\mathrm{m}$ $\mathrm{u}=-\infty$ $\mathrm{f}=?$Put the values in the above relation, we get, $\frac{1}{\mathrm{f}}=\frac{1}{-1.2}-\frac{1}{\left(-\infty \right)}$ $\frac{1}{\mathrm{f}}=-\frac{1}{1.2}$ $\mathrm{f}=-1.2m$Put the value of focal length in the power of lens formula, we get, $\mathrm{P}=\frac{1}{-1.2}$ $=\frac{-5}{6}$ $=-0.83D$So, the person suffers from Myopia, the corrective lens will be concave or diverging lens.Hence, the power is $-0.833\mathrm{D}$ should be used to restore proper vision.

Suggest Corrections
24
Explore more