Physics MCQs for NEET — Practice Questions with Answers

In an electromagnetic wave, the oscillating electric and magnetic fields are perpendicular to each other, and both are perpendicular to the direction of propagation. If propagation is along z-direction and electric field is along y-direction, then the magnetic field must be along the x-direction. (Context: 'The oscillating electric and magnetic fields, E and B are perpendicular to each other, and to the direction of propagation of the electromagnetic wave.')

The speed 'c' of electromagnetic wave in vacuum is related to $\mu_0$ and $\epsilon_0$ (the free space permeability and permittivity constants) as $c = 1/\sqrt{\mu_0\epsilon_0}$. (Context: 'The speed c of electromagnetic wave in vacuum is related to \mu_0 and \epsilon_0 (the free space permeability and permittivity constants) as follows: $c = 1/\sqrt{\mu_0\epsilon_0}$.')

Maxwell introduced the concept of displacement current to remove an inconsistency in Ampere's circuital law when dealing with time-varying fields, which led to the prediction of electromagnetic waves. (Context: 'He suggested the existence of an additional current, called by him, the displacement current to remove this inconsistency.')

When an oscillating charge (an accelerating charge) produces an oscillating electric field, it further produces an oscillating magnetic field, which in turn creates a source for an oscillating electric field, and so on. This self-sustaining oscillation is how electromagnetic waves propagate. (Context: 'The oscillating electric and magnetic fields thus regenerate each other, so to speak, as the wave propagates through the space.')

Using Maxwell's equations for $E_x$ and $B_y$, one finds that $\omega = ck$. This is the standard relation for waves. (Context: 'Using Eqs. [8.7(a) and (b)] for $E_x$ and $B_y$ and Maxwell’s equations, one finds that $\omega = ck$, where, $c = 1/\sqrt{\mu_0\epsilon_0}$ [8.9(a)]')

Maxwell formulated a set of equations involving electric and magnetic fields, and their sources, the charge and current densities. These equations are known as Maxwell’s equations. Together with the Lorentz force formula (Chapter 4), they mathematically express all the basic laws of electromagnetism. (Context: 'Maxwell formulated a set of equations involving electric and magnetic fields, and their sources, the charge and current densities... Together with the Lorentz force formula (Chapter 4), they mathematically express all the basic laws of electromagnetism.')

Electromagnetic waves with a wavelength of the order of a few metres were first produced and detected in the laboratory by Hertz in 1887. He thus verified a basic prediction of Maxwell's equations. (Context: 'Electromagnetic waves with wavelength of the order of a few metres were first produced and detected in the laboratory by Hertz in 1887.')

Electromagnetic waves are self-sustaining oscillations of electric and magnetic fields. They do not require a material medium and propagate even in vacuum, making them transverse waves. The electric and magnetic fields oscillate sinusoidally in space and time, are perpendicular to each other, and to the direction of propagation. (Context: 'They are self-sustaining oscillations of electric and magnetic fields in free space, or vacuum. They differ from all the other waves we have studied so far, in respect that no material medium is involved... The oscillating electric and magnetic fields... are perpendicular to each other, and to the direction of propagation of the electromagnetic wave.')

An oscillating charge produces an oscillating electric field, leading to an electromagnetic wave. The frequency of the electromagnetic wave naturally equals the frequency of oscillation of the charge. (Context: 'The frequency of the electromagnetic wave naturally equals the frequency of oscillation of the charge.')

According to the NCERT text, 'The external field E is not produced by the given charge(s) whose potential energy we wish to calculate. E is produced by sources external to the given charge(s).' (Section 2.8.1).