8.Electromagnetic waves
medium

$\vec E = {E_0}\hat i\,\cos \,\left( {kz} \right)\,\cos \,\left( {\omega t} \right)$ વિદ્યુતક્ષેત્ર ધરાવતા વિદ્યુતચુંબકીય તરંગ માટે ચુંબકીય ક્ષેત્ર $\vec B$ કઈ રીતે રજૂ કરી શકાય?

A

$\vec B = \frac{{{E_0}}}{C}\hat j\,\sin \,\left( {kz} \right)\,\cos \,\left( {\omega t} \right)$

B

$\vec B = \frac{{{E_0}}}{C}\hat k\,\sin \,\left( {kz} \right)\,\cos \,\left( {\omega t} \right)$

C

$\vec B = \frac{{{E_0}}}{C}\hat j\,\cos \,\left( {kz} \right)\,\sin \,\left( {\omega t} \right)$

D

$\vec B = \frac{{{E_0}}}{C}\hat j\,\sin \,\left( {kz} \right)\,\sin \,\left( {\omega t} \right)$

(JEE MAIN-2019)

Solution

$\because \overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}} \| \overrightarrow{\mathrm{v}}$

Given that wave is propagating along positive $z$ -axis and $\overrightarrow{\mathrm{E}}$ along positive $x$ -axis. Hence $\overrightarrow{\mathrm{B}}$ along $\mathrm{y}$ -axis. 

From Maxwell equation 

$\overrightarrow{\mathrm{V}} \times \overrightarrow{\mathrm{E}}=-\frac{\partial \mathrm{B}}{\partial \mathrm{t}}$

i.e. $\frac{\partial E}{\partial Z}=-\frac{\partial B}{d t}$ and $B_{0}=\frac{E_{0}}{C}$

Standard 12
Physics

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