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  • An electromagnetic wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure P on it. Which of the following statement is not true?  <div class='

An electromagnetic wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure P on it. Which of the
following statement is not true?

 

Option: 1

Radiation pressure is I/c if the wave is totally absorbed.
 


Option: 2

Radiation pressure is I/c if the wave is totally reflected.


Option: 3

Radiation pressure is 2I/c if the wave is totally reflected.
 


Option: 4

Radiated. Pressure is in the range \mathrm{I / c<p<2 I / c} for real surfaces.


Answers (1)

best_answer

Momentum per unit time per unit area =\mathrm{\frac{intensity}{speed \: of \: wave}=\frac{I}{c}}

Change in momentum per unit time per unit area \mathrm{=\Delta \mathrm{I} / \mathrm{c}=} radiation pressure \mathrm{(P) \text {, i.e. } P=\Delta I / c}

Momentum of incident wave per unit time per unit area = I/c
When wave is fully absorbed by the surface, the momentum
of the reflected wave per unit time per unit area = 0

Radiation pressure (P) = change in momentum per unit time
per unit area  =\frac{\Delta_I}{\mathrm{c}}=\frac{\mathrm{I}}{\mathrm{c}}-0=\frac{\mathrm{I}}{\mathrm{c}}

When wave is totally reflected, then momentum of the
reflected wave per unit time per unit area = –I/c
Radiation pressure (P) \mathrm{\frac{I}{c}-\left ( \frac{K}{c} \right )=\frac{2I}{c}}

Here, P lies between \mathrm{\frac{I}{c} \text { and } \frac{2 I}{c}}

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Anam Khan

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