Question

What are electromagnetic waves? Describe Maxwell’s electromagnetic theory in brief.

Answer 1

Hint: To answer this question we have to have a basic knowledge about the properties of electric and magnetic fields and how they are symmetric in nature. EM waves are waves that are created by vibrations between an electric field and a magnetic field. Or it can be said, Electromagnetic waves are composed of oscillating electric fields and magnetic fields.

Complete step by step answer: Before learning what electromagnetic waves are, we need to know the basic laws of electric and magnetic fields.
We know that an electric current produces a magnetic field and a magnetic field changing with time gives rise to an electric field. Is the converse true? Well, Maxwell argued that it is and he showed that an electric field changing with time also produces a magnetic field. However while applying the Ampere’s circuital law to find the magnetic field at a point outside a capacitor connected to a time-varying current, Maxwell noticed an inconsistency in the Ampere’s law. This inconsistency was removed by introducing an additional current called the ‘displacement current’.
The basic difference between the displacement current and conduction current is that displacement current is not the consequence of the flow of charges but it is current in the sense that it produces a magnetic field.
Maxwell worked out from his equations that variation in electric and magnetic fields would lead to a wave consisting of oscillating electric field and magnetic field perpendicular to one another and also perpendicular to the direction of propagation of the wave. Such waves are called electromagnetic waves.
Using the basic laws of electricity and magnetism, Maxwell formulated four fundamental equations.
They are:
Gauss’ law of electricity: It states that the total electric flux through any closed surface is equal to \[\dfrac{1}{{{\varepsilon _0}}}\] times that charge enclosed by the surface. It is represented as,
\[ \Rightarrow \oint {\overrightarrow E \cdot d\overrightarrow A } = \dfrac{q}{{{\varepsilon _0}}}\]
Gauss’ law of magnetism: It states that the magnetic flux through any closed surface is equal to zero. This is due to the fact that magnetic monopoles do not exist. It is represented as,
\[ \Rightarrow \oint {\overrightarrow B } \cdot d\overrightarrow A = 0\]
Faraday’s law of electromagnetic induction: It states that when the magnetic flux linked with the circuit changes with time, a current is induced in the circuit. It is mathematically represented as,
\[ \Rightarrow \varepsilon = - \dfrac{{d\phi }}{{dt}}\]
Ampere’s circuital law: The line integral of the magnetic field along a closed path is equal to \[{\mu _0}\] times the sum of the conduction current and the displacement current passing through the surface enclosed by the contour. It is represented as,
\[ \Rightarrow \oint {\overrightarrow B \cdot d\overrightarrow l = {\mu _0}\left( {{i_c} + {i_d}} \right)} \]

Note: Electromagnetic waves do not need any material medium to propagate. Light is an electromagnetic wave which is transverse in nature. All types of electromagnetic waves travel through free space with the speed of light.