Question

The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is

• A. $c:1$
• B. $c^{2}:1$
• C. $1:1$
• D. $\sqrt{c}:1$

Answer 1

Answer: (C)

$1:1$

Answer 2

: Intensity of electromagnetic wave, $I = U_{av}c$

In terms of electric field, $U_{av} = \frac{1}{2}\varepsilon_{0}E_{0}^{2}$

In terms of magnetic field, $U_{av} = \frac{1}{2}\frac{B_{0}^{2}}{\mu_{0}}$

Now $U_{av}$ (due to electric field), $= \frac{1}{2}\varepsilon_{0}E_{0}^{2}$

$= \frac{1}{2}\varepsilon_{0}(cB_{0})^{2} = \frac{1}{2}\varepsilon_{0} \times \frac{1}{\mu_{0}\varepsilon_{0}}B_{0}^{2}\left( \because\frac{E_{0}}{B_{0}} = c \right)$

$= \frac{1}{2}\frac{B_{0}^{2}}{\mu_{0}} = U_{av}$ (due to magnetic field),

Therefore, the ratio of contributions by the electric field and magnetic field components to the intensity of electromagnetic wave is 1:1.