Electromagnetic Radiation

Electromagnetic Radiation

What is Electromagnetic Radiation?

EM radiation or Electromagnetic radiation is an energy form that is present all around us and takes various forms like microwaves, radio waves, gamma rays, X-rays, etc. Electromagnetic radiation can be defined as a form of energy that is produced by the movement of electrically charged particles traveling through a matter or vacuum or by oscillating magnetic and electric disturbance. The magnetic and the electric fields come at 90° to each other and the combined waves move perpendicular to both electric and magnetic oscillating fields occurring the disturbance.

Electromagnetic Radiation

Electromagnetic Theory

Magnetism and electricity were once considered as separate forces. However in the year 1873, Clerk Maxwell, a Scottish physicist developed a unified theory of electromagnetism. Its study deals with how the electrically charged particles interact among themselves and with the magnetic field. The main electromagnetic interactions are provided in the points mentioned below.

  • Magnetic poles come in pairs that repel and attract each other, just like electric charges do.
  • The force of repulsion or attraction between two electric charges is inversely proportional to the square of the distance between the particles.
  • An electric field in motion produces a magnetic field.
  • A wire with electric current produces a magnetic field whose direction depends on the direction of the electric current.

Properties of Electromagnetic Radiation

When electromagnetic radiation occurs, the electron radiations are released as photons. These are bundles of light energy or quantized harmonic waves which travel at the speed of light. Then based on the wavelength of the electromagnetic spectrum, the energy is grouped into different categories. These magnetic and electric waves travel perpendicular to each other and have some characteristics like wavelength, amplitude, and frequency. Some basic properties of Electromagnetic Radiation are given in the points mentioned below.

Electromagnetic Radiation

  • They can travel through empty space. Waves other than electromagnetic waves have to travel through some substance. For example, sound waves will need either a solid, liquid or gas to pass through.
  • The speed of light which is 2.99792458 x 108 m/s is always constant.
  • Wavelength is commonly characterized by the symbol ‘λ’. It is the measure between the distance of either troughs or crests.

Waves and their Characteristics

Electromagnetic radiation occurs when an atomic particle, like an electron, is accelerated by an electric field, causing it to accelerate. Some waves and their Characteristics is explained briefly in the points mentioned below.


Wavelength (λ) is the distance between successive crests of a wave, especially points in an electromagnetic wave or sound wave. It can be simply defined as the distance of one full cycle of the oscillation. If ‘λ’ is the wavelength, ‘c’ is the speed of light and ‘ν‘ is frequency. Then we can derive the relation given below.

c = λ ν

The shorter the wavelength, greater the frequency and greater the frequency, higher the energy. 


It is the distance from the middle of the wave to the maximum vertical displacement of the wave.  Larger the amplitude, higher the energy and lower the amplitude, lower the energy. Amplitude tells us about the brightness or intensity of a wave compared to other waves.


The number of cycles per second is defined as Frequency. It is defined as Hertz (Hz) or sec-1. If ‘E’ is the energy, ‘h’ is Planck’s constant which is equal to 6.62607 x 10-34 and ‘ν‘ is the frequency we can derive the relation given below.

E = hν

Thus we can see that frequency is directly proportional to energy.


Period is commonly characterized by the symbol ‘T’. It is the total time which a wave takes to travel 1 wavelength.


In relation with electromagnetic radiation, the velocity is normally expressed as:

Velocity = λν
[where, ν = frequency]

The wave velocity in vacuum for electromagnetic wave is = 186,282 miles/second or 2.99×108 m/s.

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Practise This Question

A bob of mass m is suspended from the ceiling of a train moving with an acceleration a as shown in figure. Find the angle θ in equilibrium position.