Question

The solid angle subtended by the periphery of an area $1c{m}^2$ at a point situated symmetrically at a distance of 5 cm from the area is

• A. $2\times {10}^{-2}$ steradian
• B. $4\times {10}^{-2}$ steradian
• C. $6\times {10}^{-2}$ steradian
• D. $8\times {10}^{-2}$ steradian

Answer 1

The correct option is B $4\times {10}^{-2}$ steradian

Given data,

$Area=1c{m}^2$

$Distance=5cm$

$Solidangle\Omega =?$

We know the formula

Solid angle $\Omega =\frac{Area}{(Radialdistance{)}^2}$

$=\frac{1c{m}^2}{\left(5c{m}^2\right)}=\frac{1}{25}$

$=4\times {10}^{-2}steradian$

The solid angle is for $3-D$ figure like spere, cone, etc and plane angle is for plane objects or $2-D$ figure like circle,arc etc.