Question

The property which is not of an electromagnetic wave travelling in free space is that :

• A. they are transverse in nature.
• B. the energy density in electric field is equal to energy density in magnetic field.
• C. they travel with a speed equal to \(\frac{1}{\sqrt{\mu_0\epsilon_0}}\).
• D. they originate from charges moving with uniform speed.

Answer 1

The Correct Option is D

The fundamental nature of electromagnetic waves, particularly in free space, necessitates an examination of their properties. This analysis focuses on identifying which of the provided characteristics does not apply to electromagnetic waves propagating through a vacuum.

1. Electromagnetic waves are characterized as transverse. This means their electric and magnetic field components oscillate perpendicularly to the direction in which the wave travels.
2. For electromagnetic waves in free space, the energy density of the electric field is precisely equal to the energy density of the magnetic field. The total energy \(U\) is quantified by \(U = \frac{1}{2}(\epsilon_0E^2 + \frac{B^2}{\mu_0})\), where \(E\) represents the electric field strength, \(B\) denotes the magnetic field strength, \(\epsilon_0\) is the permittivity of free space, and \(\mu_0\) is the permeability of free space.
3. These waves propagate at a constant speed of \(\frac{1}{\sqrt{\mu_0\epsilon_0}}\), which is recognized as the speed of light in a vacuum, approximately \(3 \times 10^8\) m/s.
4. Electromagnetic waves are not generated by charges moving at a uniform speed. Their origin lies in accelerated charges or time-varying electric currents. This specific characteristic is the distinguishing factor because a charge moving with constant velocity does not produce changing electromagnetic fields.

Consequently, the assertion that electromagnetic waves "originate from charges moving with uniform speed" is inaccurate for waves traversing free space.