Modern Physics 7 Question 24
25. If the magnetic field of a plane electromagnetic wave is given by
$B=100 \times 10^{-6} \sin 2 \pi \times 2 \times 10^{15} t-\frac{x}{c}$,
then the maximum electric field associated with it is (Take, the speed of light $=3 \times 10^{8} m / s$ )
(Main 2019, 10 Jan I)
(a) $6 \times 10^{4} N / C$
(b) $4 \times 10^{4} N / C$
(c) $3 \times 10^{4} N / C$
(d) $4.5 \times 10^{4} N / C$
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Solution:
- Given, instantaneous value of magnetic field
$$ B=100 \times 10^{-6} \sin 2 \pi \times 2 \times 10^{15} t-\frac{x}{c} $$
and speed of light, $c=3 \times 10^{8} ms^{-1}$
For an electromagnetic wave,
$$ E _{\max }=B _{\max } \times c $$
where, $E _{\max }=$ maximum value of the electric field.
We get, $E _{\max }=100 \times 10^{-6} \times 3 \times 10^{8}=3 \times 10^{4} \frac{N}{C}$
