Test: Electromagnetic Waves - 1 - CUET Humanities MCQ

Radiowaves have the longest wavelength. The correct choice is (1).

In a E.M wave, the amplitudes of Electric field and magnetic field are related by relation.

Maxwell deduced that the speed of propagation of an electromagnetic wave through a vacuum is entirely determined by the constants μ₀ and ϵ₀ as per the following equation:
c = 

The displacement current was first postulated by Maxwell in 1861 and it was introduced on consistency consideration between Ampère's law for the magnetic field and the continuity equation for electric charges. The displacement current is not an electric current of moving free charges, but a time-varying electric field (vacuum or media), plus a contribution from the slight motion of charges bound in atoms, dielectric polarization in materials.

= 1.5 × 10^-2 m = 1.5 cm, which is choice (2).

Velocity of light in space = , where ε is the permittivity of free space and μ is the permeability of free space denoting electric and magnetic properties, respectively.

As the poynting vector,  gives the direction of the energy flow, which is in the direction of propagation.

The electric field and magnetic field of an electromagnetic wave are in phase and perpendicular (at right angles) to each other. They are also perpendicular to the direction of the EM wave.

Here, diameter of beam = 2 mm
= 2 × 10^-3 m
 Area of the beam == 
= 3.142 × 1 × 10^-6
= 3.142 × 10^-6 m²
Power, P = 10 mW = 10 × 10^-3 W
 Intensity, I = 
= 3.183 × 10³ Wm^-2

For an electromagnetic wave (in vacuum),
Velocity c = 
Air acts almost as vacuum, hence
a = 3 (approx.)