Question 1

Which of the following equations represents Maxwell's modification of Ampere's circuital law?

Accepted Answer

Maxwell found that Ampere's circuital law was inconsistent for non-steady currents. He introduced the displacement current to make it consistent, resulting in the equation $\oint \vec{B} \cdot d\vec{l} = \mu0 ic + \mu0 \varepsilon0 \frac{d\PhiE}{dt}$.

Question 2

What is the source of an electromagnetic wave?

Accepted Answer

An accelerated charge radiates electromagnetic waves because an acceleration creates a changing electric field, which in turn produces a changing magnetic field, sustaining the wave propagation.

Question 3

The speed of electromagnetic waves in vacuum is given by the relation:

Accepted Answer

The speed of light/electromagnetic waves in a vacuum is related to the permittivity ($\varepsilon0$) and permeability ($\mu0$) of free space by the formula $c = \frac{1}{\sqrt{\mu0 \varepsilon0}}.$

Question 4

Which of the following electromagnetic waves has the maximum frequency?

Accepted Answer

Gamma rays have the highest frequency and shortest wavelength in the electromagnetic spectrum.

Question 5

The ratio of the magnitude of electric field vector to magnetic field vector ($E/B$) for an electromagnetic wave is equal to:

Accepted Answer

The ratio of the amplitudes of the electric field and magnetic field in an electromagnetic wave propagating in a vacuum is equal to the speed of light, i.e., $E/B = c$.

Electromagnetic Waves — NCERT Class 12 Physics Important Questions & Revision Notes