A plane electromagnetic wave propagating in direction of unit vector hat{ n } with a speed c is desc

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8.Electromagnetic waves

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A plane electromagnetic wave propagating in the direction of the unit vector $\hat{ n }$ with a speed $c$ is described by electric and magnetic field vectors $E$ and $B$, respectively. Which of the following relations (in $SI$ units) between $E$ and $B$ can be ruled out on dimensional grounds alone?

A

$E =\frac{\hat{ n } \times B }{c}$

B

$E =-c \hat{ n } \times B$

C

$B =\frac{\hat{ n } \times E }{c}$

D

$\hat{n} \times E \times B=0$

(KVPY-2009)

Solution

(a)

As $\frac{E}{B}=c$, for an electromagnetic wave, relation $E =\frac{\hat{ n } \times B }{c}$ is dimensionally incorrect.

Standard 12

Physics

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