 ## Electromagnetic Waves: class 12

Article Topics

Displacement Current: The current which comes into play in the region, wherever the electric field and hence the electric flux is changing with time.

Ampere’s circuital law for conduction current during the charging of a capacitor was found inconsistent. Therefore, Maxwell modified Ampere’s circuital law.

## Electromagnetic Waves

Maxwell’s equations: The basic principle of electromagnetism can be formulated in terms of four fundamental equations known as Maxwell’s equations.

Electromagnetic waves: E.M. waves are those waves in which there is a sinusoidal variation of the electric and magnetic fields at right angles to each other as well as at right angles to the direction of wave propagation.

In an electromagnetic wave, the electric and magnetic fields vary with space and time and have the same frequency and are in the same phase.

### Properties

– These waves do not carry any charge.

– These waves are not deflected by electric and magnetic fields.

– They travel with the speed of light c (= 3 × 108 ms–1) in a vacuum.

– The frequency of electromagnetic waves does not change when it goes from one medium to another but its wavelength changes.

– These waves are transverse in nature, hence they can be polarised.

### Production

– Maxwell showed that an electric charge oscillating harmonically with frequency u produces electromagnetic waves of the same frequency.

– An electric dipole is a basic source of electromagnetic waves.

### The Energy Density

– Electromagnetic waves carry energy as they travel through space and this energy is equally shared by an electric field and magnetic field of electromagnetic waves.

Electromagnetic spectrum: The orderly distribution of electromagnetic radiations according to their wavelength or frequency is known as the electromagnetic spectrum.