Question

A point source of light is situated at a distance of $5$ $cm$ from a screen. There is a hole of diameter $7$ $cm$ in the screen and light of luminous intensity $15.4$ lumen passes through it. The solid angle subtended by the hole at the source will be in (str)

• A. $1.54$
• B. $2.27$
• C. $3.4$
• D. $4.7$

Answer 1

Answer: (A)

$1.54$

Solid Angle $d\omega =\frac{Area}{{distance}^2}$

$d\omega =\frac{22\times 3.5\times 3.5}{7\times 5\times 5}=1.54str$