Question: 43. The property which is not of an electromagnetic wave travelling in free space is that:
(1) they are transverse in nature.
(2) the energy density in electric field is equal to energy density in magnetic field.
(3) they travel with a speed equal to \frac{1}{\sqrt{\mu_{0} \epsilon_{0}}}
(4) they originate from charges moving with uniform speed.
Answer: Option (4)
Explanation:
Electromagnetic waves in free space are transverse waves,
in which the electric field and magnetic field oscillate perpendicular to each other
and also perpendicular to the direction of propagation.
In free space, the energy carried by an electromagnetic wave is equally shared between the electric field and the magnetic field.
Hence, the energy density in the electric field is equal to the energy density in the magnetic field.
The speed of electromagnetic waves in free space is given by
c = \frac{1}{\sqrt{\mu_{0} \epsilon_{0}}}.
Electromagnetic waves are produced by charges that are accelerating or oscillating.
Charges moving with uniform speed do not emit electromagnetic radiation.
Therefore, the statement that electromagnetic waves originate from charges moving with uniform speed is not correct,
which corresponds to option (4).