The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:
We have studied that a changing magnetic field creates an electric field. But the opposite is also true. An electric current or a time-varying electric field generates a magnetic field. This was suggested and proved by James Clerk Maxwell, who formulated a set of equations known as Maxwell’s equations. One of the most important predictions from these equations was the existence of electromagnetic waves. Electromagnetic waves are synchronised time-varying electric and magnetic fields that propagate in space. The speed of electromagnetic waves in free space is very close to the speed of light (3 x 108 m/s), which led to the conclusion that even light is an electromagnetic wave.
All wireless communications, FM radio, X-ray machines, microwave oven etc. work using these waves.
Displacement current is the current formed due to a changing electric field, and conduction current is the current carried by conductors due to flow of charges.
The Ampere-Maxwell law states that the total current passing through any surface of which the closed-loop is the perimeter is the sum of the conduction current and the displacement current. It is represented as
∮ Magnetic field * dl(very small length) = μ0 ic + μ0 ε0 dΦEdt
where B is the magnetic field, ic is the conduction current, and ΦE is the electric flux.
This proves that the laws of electricity and magnetism are more symmetrical. Faraday’s law of electromagnetic induction can be rephrased as a magnetic field changing with time gives rise to an electric field. Hence, time-dependent electric and magnetic fields give rise to each other.
Sources of Electromagnetic Waves:
Stationary charges or steady currents cannot create electromagnetic waves; they only create electrostatic fields and magnetic fields, respectively. Only accelerated charges can create these waves. A charge oscillating with some frequency produces an oscillating electric field in space. This produces an oscillating magnetic field, which, in turn, creates an oscillating electric field and so on. Thus, the oscillating electric and magnetic fields are regenerating each other, and this electromagnetic wave propagates in space. The frequency of this wave is equal to the frequency of oscillation of the charge.
Nature of Electromagnetic Waves:
The electric and magnetic fields in these waves are perpendicular to each other as well as to the direction of propagation. In free space or vacuum, these waves are self-sustaining oscillations of their electric and magnetic fields. And there is no material medium involved in the vibrations of these fields. The velocity of these waves in free space or vacuum is constant. Electromagnetic waves are polarised and can be diffracted and refracted.
Total Energy of an Electromagnetic Wave:
Electromagnetic waves also carry energy and momentum like other waves when they move through space. The energy is shared through their magnetic and electric fields. When these waves strike the surface, along with total energy, the pressure is also exerted on it.
When electromagnetic waves were predicted to exist, the only known electromagnetic waves were light waves. Today we are aware of X-rays, gamma rays, radio waves, microwaves, ultraviolet and infrared waves apart from light waves. The electromagnetic spectrum is the classification of electromagnetic waves based on frequency.
Our day-to-day life depends on using the internet on our phones and laptops, making calls, watching TV etc. This is only possible because of electromagnetic waves, which forms the foundation of modern-day technology. Maxwell’s equations were also used to form the basis of Electromagnetic wave equation, Maxwell’s wave equations and Helmholtz wave equation that have many other applications. Check out this concept visualized further more details in on the MSVgo app.