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(B) For a monochromatic electromagnetic wave in free space:$1$. Electric and magnetic fields oscillate in phase,so the phase difference is $0$,not $\f

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Only $2$

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(B) For a monochromatic electromagnetic wave in free space:$1$. Electric and magnetic fields oscillate in phase,so the phase difference is $0$,not $\frac{\pi}{2}$. Statement $1$ is incorrect.$2$. The energy density of the electric field is $u_E = \frac{1}{2} \epsilon_0 E^2$ and the magnetic field is $u_B = \frac{1}{2\mu_0} B^2$. Since $E = cB$ and $c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$,it follows that $u_E = u_B$. Thus,energy is distributed equally. Statement $2$ is correct.$3$. The radiation pressure $P$ is given by $P = \frac{I}{c} = u_{avg}$,where $u_{avg}$ is the average energy density. It is not the product of speed and energy density. Statement $3$ is incorrect.$4$. The speed of the wave $c$ is given by $c = \frac{E}{B}$. Statement $4$ is incorrect as it states the ratio of magnetic to electric field $(B/E = 1/c)$.Therefore,only statement $2$ is correct.

Similar Questions

$A$ plane electromagnetic wave of frequency $25 \text{ MHz}$ travels in free space along the $X$-direction. At a particular point in space and time,the magnetic field is $\overrightarrow{B} = 2.1 \times 10^{-8} \hat{k} \text{ T}$. Find the electric field $\overrightarrow{E}$ at this point.

The Poynting vector $\vec S$ is defined as a vector whose magnitude is equal to the wave intensity and whose direction is along the direction of wave propagation. Mathematically,it is given by $\vec S = \frac{1}{{\mu _0}}(\vec E \times \vec B)$. Show the nature of the $\vec S$ vs $t$ graph.

Assertion $(A)$: Electromagnetic waves exert pressure,called radiation pressure.
Reason $(R)$: This is because they carry energy.

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