Question

A lamp delivers a luminous flux of $100\, W$ to an absorber of area $1\,cm ^{2}$. The force due to radiation pressure is

• A. $3.3 \times 10^{-4} \,N$
• B. $16.5 \times 10^{-7} \,N$
• C. $3.3 \times 10^{-6}\, N$
• D. $3.3 \times 10^{-7} \,N$

Answer 1

Answer: (D)

$\because$ Force $=$ Rate of change of linear momentum
$F=\frac{d p}{d t}=\frac{d}{d t}\left(\frac{v}{c}\right)=\frac{1}{c} \frac{d v}{d t}$
where, $v=$ electromagnetic wave energy.
or $F=\frac{I}{c}=\frac{100}{3 \times 10^{8}}=33.3 \times 10^{-8} \,N$
or $ F=3.3 \times 10^{-7} \,N$