A man can see only between 75 cm and 200 cm. The power of lens to correct the near point will be

Question

A man can see only between 75 cm and 200 cm. The power of lens to correct the near point will be (A) +8/3 D (B) + 3 D (C) - 3 D (D) -8/3 D

Tardigrade Admin · Accepted Answer

For improving near point, convex lens is required and for this convex lens u=-25 cm , v=-75 cm ∴ (1/f)=(1/-75)-(1/-25) ⇒ f=(75/2) cm So power P=(100/f) =(100/75 / 2)=+(8/3) D

Q. A man can see only between $75 c m$ and $200 c m$ . The power of lens to correct the near point will be

+8/3 D

+ 3 D

- 3 D

-8/3 D

For improving near point, convex lens is required and for this convex lens
$u = - 25 c m, v = - 75 c m$
$∴ \frac{1}{f} = \frac{1}{- 75} - \frac{1}{- 25}$
$\Rightarrow f = \frac{75}{2} c m$
So power $P = \frac{100}{f}$
$= \frac{100}{75/2} = + \frac{8}{3} D$

Q. A man can see only between 75cm and 200cm. The power of lens to correct the near point will be