A man's near point is 0.5 m and far point is 3 m . Power of spectacle lenses required for (i) reading purposes (ii) seeing distant objects, respectively are

Question

A man's near point is 0.5 m and far point is 3 m . Power of spectacle lenses required for (i) reading purposes (ii) seeing distant objects, respectively are (A) -2 D and +3D (B) +2 D and -3D (C) +2 D and -0.33D (D) -2 D and +0.33D

Tardigrade Admin · Accepted Answer

For reading purpose u=-25 cm,v=-50 cm, f=? ∴ (1/f)=(1/v)-(1/u)=(1/50)+(1/25)=(1/50) P=(100/f)=+2D For distinct vision, fâ²= distance of far point =-3 m P = (1/f â²)=-(1/3) D = - 0.33D

Q. A man's near point is $0.5 m$ and far point is $3 m$ . Power of spectacle lenses required for

(i) reading purposes

(ii) seeing distant objects, respectively are

$- 2$ $D$ and $+ 3 D$

$+ 2$ $D$ and $- 3 D$

$+ 2$ $D$ and $- 0.33 D$

$- 2$ $D$ and $+ 0.33 D$

For reading purpose
$u = - 25 c m, v = - 50 c m, f = ?$
$∴ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} = \frac{1}{50} + \frac{1}{25} = \frac{1}{50}$
$P = \frac{100}{f} = + 2 D$
For distinct vision,
$f^{'} =$ distance of far point $= - 3$ $m$
$P$ = $\frac{1}{f '} = - \frac{1}{3}$ $D$ = $-$ $0.33 D$

Q. A man's near point is 0.5m and far point is 3m . Power of spectacle lenses required for (i) reading purposes (ii) seeing distant objects, respectively are

−2 D and +3D

+2 D and −3D

+2 D and −0.33D

−2 D and +0.33D