Q154 / 160 · AP EAMCET 2023 (19 May Shift 1) · Physics

Electromagnetic waves of energy flux $75 \times 10^4$ $\mathrm{Wm}^{-2}$ incidents normally on a surface of area $40 \mathrm{~cm}^2$. If absorbs the surface the flux completely, the total momentum delivered to the surface in one second is

  • A
    $10^{-2} \mathrm{kgms}^{-1}$
  • B
    $10^{-3} \mathrm{kgms}^{-1}$
  • C
    $10^{-4} \mathrm{kgms}^{-1}$
  • Correct answer
    D
    $10^{-5} \mathrm{kgms}^{-1}$

Solution

$\begin{aligned} & \text { Momentum transferred }=\text { Force } \times \text { time } \\ & =\frac{I}{\mathrm{C}} \times \text { A Pressure } \times \text { Area } \times \Delta \mathrm{t}=\frac{\mathrm{I}}{\mathrm{C}} \times \mathrm{A} \times \Delta \mathrm{t} \\ & =\frac{75 \times 10^4}{3 \times 10^8} \times 40 \times 10^{-4} \times 1=10^{-5} \mathrm{kgms}^{-1}\end{aligned}$

Hence, the correct answer is option: 'D'.

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