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

Hint: Electromagnetic waves are created by the vibrations of electric fields and magnetic fields. They are transverse. That is, the direction of the electric field, magnetic field, and direction of propagation are perpendicular to each other. The energy in an electromagnetic wave is divided on average equally between magnetic and electric fields.

Complete answer:
Electromagnetic energy is carried by electromagnetic waves. The energy store in the electromagnetic wave is the sum of energy in the electric field and magnetic field. The energy density of an electromagnetic wave is given below.
Energy stored in the electric field and the magnetic field is given below.
${U_e} = \dfrac{1}{2}{\varepsilon _0}{E^2}$
Here, ${\varepsilon _o}$is the permittivity of free space, $E$is the electric field.
And
${U_m} = \dfrac{1}{2}\dfrac{{{B^2}}}{{{\mu _o}}}$
Here, the permeability of the medium is ${\mu _o}$ and $B$ is the magnetic field.
Therefore, the energy density of electromagnetic waves is summing both.
$U = {U_e} + {U_m} = \dfrac{1}{2}{\varepsilon _o}{E^2} + \dfrac{1}{2}\dfrac{{{B^2}}}{{{\mu _o}}}$ ……………………..(1)
These energies are equal as below.
$\dfrac{1}{2}{\varepsilon _o}{E^2} = \dfrac{1}{2}\dfrac{{{B^2}}}{{{\mu _o}}}$
Hence, equation (1) can be written as below.
$U = {\varepsilon _o}{E^2} = \dfrac{{{B^2}}}{{{\mu _o}}}$
Therefore, the contribution of the electric field and the magnetic field is the same. So, the ratio of contributions of the electric and magnetic fields is $1:1$.
Hence, option (C) is the correct option.

Note:
An electromagnetic wave is radiated by an oscillating or accelerated charge in which an electric field is produced by the changing of the magnetic field and also, a magnetic field is produced by the changing in the electric field.
The electromagnetic field is classified by wavelength or frequency called the electromagnetic spectrum.
Electromagnetic waves are predicted by Maxwell's equations of motion.