Question

A person near point is $50cm$ and his far point is $3m$. Powers of the lenses he requires for
(i) reading
(ii) seeing distant stars are

• A. $-2D$ and $0.33D$
• B. $2D$ and $0.33D$
• C. $-2D$ and $3D$
• D. $2D$ and $-3D$

Answer 1

The correct option is D $2D$ and $-3D$

For correcting the near point, required focal length
$f=\frac{50\times 25}{(50-25)}=50cm$
So power $P=\frac{100}{50}=+2D$
For correcting the far point, required focal length
$f=-$ ( defected far point ) $=-3m$
$\therefore P=-\frac{1}{3}D=-0.33D$