Transverse Nature of Electromagnetic Waves

Electromagnetic waves are travelling waves in which electric and magnetic fields are perpendicular to each other. The direction in which electromagnetic waves travel is also perpendicular to the direction of electric and magnetic fields. Therefore, the nature of electromagnetic waves is transverse.

The basic sources of electromagnetic waves are -

• An electric charge at rest only produces an electric field around it but not a magnetic field.
• A charge moving with uniform velocity produces both electric and magnetic fields but of static nature.
• An accelerating charge and oscillating charge produces both electric field and magnetic field which varies with time. 
• Hence the accelerating and oscillating charge is the basic source for the production of electromagnetic waves.

Key Terms: Electromagnetic waves, Transverse waves, Longitudinal Waves, Electric flux, Magnetic field, electric field

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Electromagnetic Waves

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According to Faraday's law of electromagnetic induction, a changing magnetic field with time gives rise to an electric field which also changes with time.

Maxwell pointed out, there is symmetry in nature. Therefore, a changing electric field also produces a changing magnetic field.

He concluded that:

• The changing electric and magnetic fields create a disturbance in space which has wave-like characteristics.
• These waves propagate through space without using any physical medium and are referred to as Electromagnetic waves.

Since, these electric and magnetic fields are perpendicular to each other and the direction of propagation of electromagnetic waves are perpendicular to both. Hence, electromagnetic waves are referred to as Transverse in nature.

The figure below clearly represents the direction of propagation of an electromagnetic wave which is perpendicular to both electric and magnetic fields.

Electromagnetic Waves

History of Electromagnetic Waves

Maxwell was the first to predict the presence of electromagnetic waves

• Hertz produces and detected electromagnetic waves of wavelength 6 m experimentally.
• J.C. Bose produced electromagnetic waves of wavelength ranging from 5 mm to 25mm.
• Marconi successfully transmitted the electromagnetic wave up to a few kilometers.

Some of the examples of electromagnetic waves are visible light rays, Ultraviolet rays, X- rays, Microwave rays, Radio waves and Gamma rays (ℽ- rays)

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Transverse Wave and Longitudinal Wave

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There are two types of waves: 1) Transverse waves 2) Longitudinal waves.

Transverse waves

• Transverse waves are the waves in which the constituents of the medium oscillate perpendicular to the direction of wave propagation.
• All electromagnetic waves are transverse waves.

Longitudinal waves

• Longitudinal waves are the waves in which the constituents of the medium oscillate along the direction of wave propagation.
• Sound waves are longitudinal waves.

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Transverse Nature of Electromagnetic waves

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When a charge accelerates or oscillates a time varying electric and magnetic field develops that are perpendicular to each other.

• Due to this oscillating electric and magnetic field, a disturbance is created in space.
• This disturbance travels along the direction perpendicular to oscillating electric and magnetic fields.
• This gives rise to electromagnetic waves which propagate perpendicular to both electric and magnetic fields.
• In a transverse wave, the constituents of the medium oscillate perpendicular to the direction of wave propagation.
• Due to this fact, we conclude that electromagnetic waves are Transverse in nature.

Evidence of Transverse nature of electromagnetic waves by phenomenon of Polarization

• Light is also a form of electromagnetic waves. The oscillation of electric and magnetic fields can occur in numerous planes.
• A light wave that is vibrating in more than one plane is known as unpolarized light.
• Polarized light waves are those in which the vibrations occur in a single plane.
• The process of transforming unpolarized light into polarized light is known as polarization.
• Polarization explains the transverse nature of electromagnetic waves, as the polarization only works for transverse waves but not for longitudinal waves.
• Therefore, the transverse nature of the electromagnetic wave is evident by the phenomenon of polarization.

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Proof of Transverse Nature of Electromagnetic Waves

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Consider a plane electromagnetic wave traveling along x- direction passing through an imaginary cube.

Let electric field intensity at face ABCD is E and at face EFGH is E’.

According to Gauss’ Law, the total electric flux across the cube is zero because it does not enclose any charge.

Since Electric field intensity at face ABCD of the cube is E and at face EFGH is E', therefore, we can write above equation as,

The above equation shows that the value of the x- component of the electric field does not change with time, that means the y- component of the electric field will change. Hence, the electric field is perpendicular to the direction of propagation of the wave.

Similarly, it can be proved that the magnetic field is perpendicular to the direction of propagation of the wave.

Since, both electric and magnetic fields are perpendicular to the direction of the wave. So, “electromagnetic waves are transverse in nature”.

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Things to Remember

• Electromagnetic waves propagate perpendicular to the direction of mutually perpendicular electric and magnetic fields.
• Accelerating and oscillating charges are the sources of electromagnetic waves.
• In Transverse waves, the constituents of the medium oscillate perpendicular to the direction of wave propagation.
• Polarization of light is also evidence of the transverse nature of electromagnetic waves.
• All electromagnetic waves are transverse in nature.
• Maxwell was the first to predict the presence of electromagnetic waves.