Question

What is the power of the eye glasses worn by a person whose far point is 5 m?

Answer 1

When the object object distance is infinite ,A virtual image has to be formed at far point.

$u=\infty$ and $v$=-5m$

So $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

$\frac{1}{f}=\frac{1}{-5}-\frac{1}{\infty }$

SO $F=-5m$

Power of eye glass is $P=\frac{1}{f}=1/-5=-0.2D$