**NEET Physics Notes Electromagnetic Wave – Electromagnetic Waves and their Characteristics**

** Electromagnetic Waves and their Characteristics**

**Electromagnetic Waves and their Characteristics**

Electromagnetic waves are those waves, in which electric and magnetic fields vary sinusoidally in space and with time. The electric and magnetic fields are mutually perpendicular to each other and each field is perpendicular to the direction of propagation of the wave.

Maxwell’s theory predicted that electromagnetic waves of all frequencies (and hence all wavelengths) propagate in vacuum, with a speed given by

where, **μ _{0}** is the magnetic permeability and

**ε**is the electric permittivity of vacuum. Now, for the vacuum, and Substituting these values in the above relation, we have

_{0}All the electromagnetic waves are of the transverse nature whose speed depends upon the medium but their frequency does not depend on the medium.

Transverse waves can be polarised.

Energy is being transported with the electromagnetic waves.

**Conduction Current**

It is a current in the electric circuit, which arises due to the flow of electrons in the connecting wires of the circuit, in a definite closed path.

**Maxwell’s Displacement Current**

It is that current which comes into play in the region, whenever the electric field and hence the electric flux is changing with it.

**Mechanical and Non-mechanical Waves**

Waves requiring a medium to propagate are called mechanical waves such as sound waves, while the waves do not require a medium to propagate are called the non-mechanical waves, such as electromagnetic waves.

**Maxwell’s Equations**

Maxwell in 1862, gave the basic laws of electricity and magnetism in the form of four fundamental equations, which are known as Maxwell’s equations. In the absence of any dielectric and magnetic material, the Maxwell’s equations are based on experimental observations followed by all electromagnetic phenomena, may be stated in the integral form as given below

**Gauss’s law for electrostatics**

This law gives the total electric flux in terms of charge enclosed by the closed surface.

This law states that the electric lines of force start from positive charge and end at negative charge i.e. the electric lines of force do not form a continuous closed path.

Mathematically

**Gauss’s law for magnetism**

This law shows that the number of magnetic lines of force entering a closed surface is equal to number of magnetic lines of force leaving that closed surface.

This law tells that the magnetic lines of force form a continuous closed path.

This law also predicts that the isolated magnetic monopole does not exist.

Mathematically,

**Faraday’s law of electromagnetic induction**

This law gives a relation between electric field and a changing magnetic flux.

This law tells that the changing magnetic field is the source of electric field.

Mathematically,

**Ampere-Maxwell’s law**

This law states that the ipagnetic field can be produced by a conduction current as well as by displacement current.

This law also states that the conduction current and displacement current together have a property of continuity.

At an instant, in a circuit, the conduction current is equal to displacement current.

Mathematically,

These equations are collectively called Maxwell’s equations