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Electromagnetic Waves

Grade 8
May 31, 2023

Introduction of an Electromagnetic Wave

The space between the Sun and Earth is almost empty or a vacuum. Different types of waves, called electromagnetic waves, carry energy from the Sun to Earth. Electromagnetic waves (light waves) are non-mechanical waves; they don’t require any medium to travel. They can even travel through a vacuum. Electromagnetic waves don’t require matter to transfer energy.

Source of an Electromagnetic Wave:

Electromagnetic waves are produced by charged particles that are in motion or vibrating. Charged particles like 𝝰-particles, electrons, and protons can travel through the vacuum or through matter.

Electromagnetic waves are made up of two parts-

  • Electric field
  • Magnetic field
electromagnetic wave

Electric and magnetic fields are force fields. As they exert non-contact force on the objects.

For example-: The Earth is surrounded by a gravitational field, which is a force field. This field exerts a force on all objects that have mass.


Similarly, a magnetic field exerts a force on another magnet or magnetic material. Magnetic fields cause other magnets to line up along the direction of the magnetic field.

An atom is made up of positively charged protons, uncharged neutrons, and negatively charged electrons. A charged particle is surrounded by an electric field.

A charged particle at rest is surrounded only by an electric field. But a moving charged particle is also surrounded by a magnetic field. Example-: A wire in which electrons are flowing that carries an electric current is surrounded by a magnetic field. A moving charged particle is surrounded by electric and magnetic fields.

A charged particle in motion is surrounded by an electric and a magnetic field

When we shake a rope up and down, we generate a wave that moves away from our hand. When a charged particle vibrates up and down, it generates a charging electric and magnetic field that moves away from the vibrating charge in all directions.

A vibrating charged particle generates changing electric and magnetic fields

Terms Related to Electromagnetic Waves:

Like all waves, an electromagnetic wave is described by some terms like:

  • Wavelength
  • Time period
  • Frequency
  • Speed


An electromagnetic wave is made by a vibrating charged particle. When the charged particle makes one complete vibration, one wavelength is made. It is denoted by λ. Its unit is a meter (m).

Wavelength of an electromagnetic wave


Frequency is the number of times a charged particle makes complete vibrations in 1 second. It is denoted by f or ν. Its unit is Hertz (Hz).

Frequency of an electromagnetic wave

Time Period:

The time period is the time taken by a charged particle to complete one vibration. It is denoted by T. Its unit is sec.

Time period = 1/ frequency

Time period of an electromagnetic wave


Speed of an electromagnetic wave = (wavelength)/(time period)

Speed of an electromagnetic wave = V = λ/( T)

Speed of an electromagnetic wave = frequency × wavelength

V = f × λ

Speed of an electromagnetic wave

All electromagnetic waves travel through space at the same speed, about 300,000 km/s, 300000000 m/s, or 186,000 miles per hour. This speed is sometimes called the speed of light. Electromagnetic waves travel at different speeds in different materials. They usually travel more slowly in solids and faster in gases.

Speed of an electromagnetic wave in different media

The Energy of Electromagnetic Waves:

  • Like all waves, electromagnetic waves transfer energy from one place to another.
  • Different electromagnetic waves transfer different amounts of energy. The amount of energy depends on the frequency of the wave.
  • Electromagnetic waves with higher frequencies have more energy.
Energy of an electromagnetic wave


Calculate the frequency of an electromagnetic wave whose time period is 2 nanoseconds.


Time period = 2 nanosecond

The frequency is given by ν = 1/T

Therefore, frequency = 1/(2×10-9)

frequency = 0.5 GHz


Calculate the time period of the sound wave whose frequency is 20 MHz.


Frequency = 20 MHz

The frequency is given by ν = 1/T

Thus, the time period is given by T = 1/ν

Therefore, time period = 1/(20MHz) time period = 0.05 x 10-6 s

Electromagnetic Waves


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