First slide

Electromagnetic waves and its nature

Question

The amplitude of the electric field in a parallel beam of plane electromagnetic waves of intensity $53.1 W m^{- 2}$ is (permittivity of free space= $8.85 \times 10^{- 12} C^{2} / N m^{2}$ )

Moderate

A

$20 V m^{- 1}$
B

$200 V m^{- 1}$
C

$400 V m^{- 1}$
D

$40 V m^{- 1}$

Solution

Intensity of electromagnetic wave in terms of maximum electric field is
$I = \frac{1}{2} \in_{0} E_{0}^{2} C \Rightarrow E_{0} = \sqrt{\frac{2 I}{\in_{0} C}} \Rightarrow E_{0} = \sqrt{\frac{2 \times 53.1}{8.85 \times 10^{- 12} \times 3 \times 10^{8}}} \Rightarrow E_{0} = \sqrt{\frac{2 \times 53.1 \times 10^{4}}{26.55}} = \sqrt{4 \times 10^{4}} \Rightarrow E_{0} = 200 V m^{- 1}$

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