NCERT Solutions for Class 12 Physics Electromagnetic Waves Notes

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Electromagnetic waves: The waves propagating in space through electric and magnetic fields varying in space and time simultaneously are called electromagnetic waves.

An electromagnetic wave consists of a fluctuating electric field and a fluctuating magnetic field of the same frequency and the same phase.
The electric and magnetic fields are mutually perpendicular and also perpendicular to the direction of propagation of the wave.
In the propagation of an electromagnetic wave, a varying electric field E gives rise to a varying magnetic field and so on. In this way, electric and magnetic fields of the wave sustain each other.

How are Electromagnetic waves produced?

Electromagnetic waves are produced by an accelerated or de-accelerated charge or LC circuit.

Transverse Nature of Electromagnetic waves:The Electromagnetic waves are transverse in nature with the electric and magnetic fields perpendicular to the direction of propagation.

If the electric field is along the y-axis and magnetic field is along the z-axis then the direction of propagation of the wave is along the x axis.

For the videos and notes on more topics, click on Physics notes for Class 12.

Characteristics of electromagnetic waves:

The electromagnetic waves travel in free space with speed of light irrespective of their wave length.
Electromagnetic waves are transverse in nature.
Electromagnetic waves do not need a material medium for their

propagation.

Electromagnetic waves are produced by accelerated charges.
Electromagnetic waves obey the principle of superposition.

Electromagnetic waves are neutral so they are not deflected by electric and magnetic fields.
The ratio of magnitudes of electric and magnetic field vectors in free space is constant and equal to c

ie c = E/B = 3×10⁸m/s

Electromagnetic waves show properties of reflection, refraction, interference,

diffraction and polarisation.

What is meant by electromagnetic spectrum?

It is an orderly arrangement of electromagnetic waves from radio waves of largest wave length to gamma rays of shortest wave length.

Uses of Electromagnetic waves

Radiowaves: Used for communication using radio, T V, cellular phone etc
Microwaves: Used in RADAR, Satellite communication, mobile phone, microwave oven.
Infrared Radiation: Infrared camera, physiotherapy, for determination of molecular structure.
Visible light: To see objects.
Ultraviolet Radiations: Helps to produce vitamin D in our skin. Used in water purifiers, used to sterilize drinking water and surgical instruments.
X-Rays: To take X ray photograph of the human body, to detect fracture in bones, to detect the presence of stone in gallbladder and kidney, to study crystal structure.
Gamma Rays: Study of Nuclear Structure, radiotherapy.

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