Question

Assertion: In electromagnetic waves electric field and the magnetic field are perpendicular to each other.
Reason: Electric field and the magnetic field are self-sustaining.
A. Both the assertion and reason are correct and the reason is the correct explanation of the assertion
B. Both the assertion and reason are correct but reason is not the correct explanation for assertion
C. assertion is correct but reason is incorrect
D. Both the assertion and reason are incorrect

Answer 1

Hint: Electromagnetic wave is a combination of two fields which are perpendicular to each other and to the direction of propagation and they are not dependent on anything other than electric and magnetic fields that is the reason they are self-sustaining.

Complete answer:
Before discussing anything we should know something about an electromagnetic wave. As the word suggests “Electromagnetic waves are waves that are created as a result of sinusoidal vibrations between an electric field and a magnetic field”. The electric field and magnetic field of an electromagnetic wave are perpendicular (at right angles) to each other. Not only this, they are perpendicular to the direction of the propagation of the electromagnetic wave.

The perpendicular behavior of the electric and magnetic field in an EM wave can be understood by Maxwell’s equations
We know that, the direction of propagation is EM wale is given by,

$\begin{align}
  & \hat{n}=\hat{E}\times \hat{B} \\
 & \hat{n}=E\centerdot B\sin \theta \\
\end{align}$

For the maximum value

$\begin{align}
  & \sin \theta =1 \\
 & {{\sin }^{-1}}1=90{}^\circ \\
\end{align}$

Thus, the electric and magnetic fields are perpendicular to each other.
From the explanation we can conclude that, assertion and reason both are true statements but the reason is not the correct explanation of the assertion.

So, the correct answer is “Option B”.

Additional Information:
An electromagnetic wave travels at a velocity of $3\times {{10}^{8}}{m}/{s}\;$. EM vales (ex. visible light) are capable of showing interference or diffraction. An electromagnetic wave can travel through anything they don’t need a medium to propagate or travel from one point to another. They are not dependent on other factors therefore electric and magnetic fields are self-sustaining.

Note:
Electromagnetic waves are self-propagating and their speed does not depend on the medium through which they are traveling. Electromagnetic radiations have both waves like nature and particles like nature. Wave nature of EM radiation is explained by the optical behavior or the light.