Question

Light with an energy flux of $9Wc{m}^{-2}$ falls on a non-reflecting surface at normal incidence. If the surface has an area of $20c{m}^2$. The total momentum delivered for complete absorption in one hour is:

• A. $2.16\times {10}^{-4}kgm{s}^{-1}$
• B. $1.16\times {10}^{-3}kgm{s}^{-1}$
• C. $2.16\times {10}^{-3}kgm{s}^{-1}$
• D. $3.16\times {10}^{-4}kgm{s}^{-1}$

Answer 1

The correct option is C $2.16\times {10}^{-3}kgm{s}^{-1}$

We know that: $I=\frac{E}{At}$

$\Rightarrow 9=\frac{E}{20\times 3600}$

$\Rightarrow E=9\times 20\times 3600$

$\Rightarrow P=\frac{E}{C}=2.16\times {10}^{-3}kgm{s}^{-1}$