Question

a person is unable to see objects distinctincly placed within 50cm from his eyes assuming the near point of normal human eye to be 25 cm calculate the power of lens to correct the defect​

Answer 1

Answer

Given=>

- The person is suffering from a disorder of eye called Hypermetropia in which a person can't see the nearby objects clearly.

-Hypermetropia is also called farsightedness.

-It can be fixed by using a convex lens of proper power.

Now, according to the question=>

u(object distance) = -25cm

v(image distance) = -50cm.

now, by using lens formula=>

$\dfrac{1}{v}$ - $\dfrac{1}{u}$ = $\dfrac{1}{f}$

=>$\dfrac{-1}{50}$ +$\dfrac{1}{25}$ = $\dfrac{1}{f}$

=>2-$\dfrac{1}{50}$ = $\dfrac{1}{f}$

=>f = 50cm

=>f = +0.5m.

Now, We know that=>

Power = $\dfrac{1}{f}(in metre)$

=>P =$\dfrac {1}{0.5}$

=>P =+ 2 dioptre.

Hence the person should use a convex lens of +2D power.