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Characteristics of Electromagnetic Waves

Last Updated : 08 Mar, 2022
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Electromagnetic (EM) waves are waves that are related to both electricity and magnetism. These waves travel in space and are made up of time-varying electric and magnetic fields. An electromagnetic wave is a wave radiated by an accelerating or oscillatory charge in which a varying magnetic field is the source of the electric field and a varying electric field is the source of the magnetic field. Thus, the two fields become sources of each other and the wave propagates sinusoidally in a direction perpendicular to the two fields.

What are Electromagnetic Waves?

Linearly Polarised Electromagnetic Waves

Electromagnetic (EM) waves are waves that are associated with both electricity and magnetism. Electromagnetic (EM) waves are waves that change periodically in an electric and magnetic field that spreads through space. Waves are accompanied by lightning and captivity and as they are waves so they will spread through space. When electric and magnetic fields join together and when they vary over time they will give rise to electromagnetic waves. 

The electromagnetic equations emerged from Maxwell’s equations. Maxwell has introduced these EM waves with special parcels that can be used for many practical Objectives. Unlike time, the electric field is a time-varying magnetic field of electromagnetic waves. Electromagnetic swells are coupled with time-varying electric and magnetic fields that propagate in space.

Characteristics of Electromagnetic waves

  • The electric field varies with time, and it will give rise to a magnetic field, this magnetic field varies with time and it gives rise to the electric field and the process continues like this.
  • These electric and magnetic fields vary periodically and are coupled with each other when concurrently propagating in space giving rise to electromagnetic waves.
  • The magnetic field will be a sine wave but in a direction perpendicular to the electric field. Both of these provide advancement to the electromagnetic field.
  • However, the magnetic field along the y-axis, the wave will also propagate in the z-axis if the electric field is along the x-axis.
  • The electric and magnetic fields are each distinct and perpendicular to the direction of surge propagation.
  • Electric and magnetic fields that are opposite in time and linked to each other give rise to electromagnetic waves.

Nature of Electromagnetic waves

  • EM waves are transverse waves. The transverse waves are those in which the direction of disturbance or displacement in the medium is vertical to that of the propagation of the wave.
  • The patches of the medium are moving in a direction vertical to the direction of propagation of the wave. In the case of EM waves, the propagation of waves takes place along the x-axis, electric and magnetic fields are vertical to the wave propagation. This means surge propagation x-axis, electric field y-axis, magnetic field z- axis.
  • Because of this EM waves are transverse waves in nature. The electric field of EM surge is represented as

Ey = E0 sin(kx– wt) 

Where Ey = electric field along the y-axis and x = direction of propagation of the wave.  

  • Wave number k = (2π/λ)
  • The magnetic field of the EM wave is represented as

Bz = B0sin(kx− wt)

Where BZ = electric field along the z-axis and x = direction of propagation of the wave.

B0 = (E0/c)

Then, we observe some electromagnetic waves. In free space or vacuum, they are self-perpetuating electric and magnetic field fluctuations. The vibrations of the electric and magnetic fields are unlike any different waves that we have seen from afar, in that there is no physical medium involved. Longitudinal contraction and rarefaction waves are contraction and rarefaction waves in the air. A rigid, shear-resistant solid can produce transverse elastic(sound) waves correspondingly.

Sources of Electromagnetic Waves

EM waves are generated by electrically charged particle oscillates ( accelerating charges). The electric field consociated with the quickening charge vibrates which generates the vibrating magnetic field. These both vibrating electric and magnetic fields give advancement to EM swells

Still, the electric field fraternized with the charge will correspondingly be stationary, If the charge is at rest. There will be no generation of EM waves as the electric field isn’t differing with time.

When the charge is moving with even velocity, also the acceleration is 0. The alteration in electric field with time is also constant as a result again there will be no electromagnetic waves generated. This shows that only the accelerated charges alone can induce EM waves.

Applications of Electromagnetic Waves

  • One of the most consequential uses of electromagnetic waves is in communication.
  • We can perceive everything around us because of electromagnetic waves.
  • It assists in aircraft navigation and assists the pilot for sophisticated take-off and landing of aircraft. It also helps to compute the speed of the aeroplane.
  • It has indeed found consequent applications in the medical field. For example X-rays in beam, radio, and TV broadcast signals in eye surgery. These signals are transmitted by electromagnetic waves.
  • Electromagnetic swells help to determine the speed of transient vehicles.
  • They are used for electronic devices such as TVs. are used in. Remote, Remote Buses, LED Television, Fryer Range, etc.
  • Voice transmission can be achieved in mobile phones due to electromagnetic waves.

Sample Questions

Question 1: Name the electromagnetic radiation which can be generated by a klystron or magnetron valve.

Answer:

The electromagnetic wave generated by the klystron or magnetron valve is a microscope.

Question 2: Why is the ozone layer at the top of the stratosphere important for human existence?

Answer:

The ozone layer at the top of the stratosphere is important for human survival because the ozone layer at the top of the stratosphere traps most of the ultraviolet rays coming from the sun and blocks the harmful effects of ultraviolet rays.

Question 3: How does an oscillating charge produce electromagnetic waves?

Answer:

An oscillating charge generates an oscillating electric field and an oscillating electric field generates a magnetic field which then generates an oscillating electromotive force. An oscillating voltage produces an oscillating magnetic field and so on. In this way, the oscillating charges generate an electromagnetic wave.

Question 4: How are electromagnetic waves generated?

Answer:

A changing electric field generates a magnetic field and a changing magnetic field produces an electric field, the result is a wave of electric and magnetic fields that propagates through space. These propagating fields are called electromagnetic waves.

Question 5: State Lenz’s law. A metal rod placed horizontally in the east-west direction is allowed to fall under gravity. Will the emf be induced at its ends? justify your answer.

Answer:

Lenz’s law states that the induced emf of an induced current in a circuit is always opposed to the cause that produces it. Yes, the electromotive force will be induced in the rod as the magnetic flux changes. When a metal rod placed horizontally in the east-west direction is allowed to fall freely under gravity i.e. falls from north to south, the intensity of the magnetic lines of the earth’s magnetic field is changed through the medium, i.e. the magnetic flux changes and hence the induced emf in this.

Question 6: Write Faraday’s law of electromagnetic induction.

Answer:

Based on the experiment, Faraday gave the following two laws: First Law Whenever the magnetic flux associated with a circuit changes, an emf is induced in it which lasts as long as there is a constant change in the flux.

The second law is that the emf induced in a loop or closed circuit is directly proportional to the rate of change of the magnetic flux associated with the loop. i.e. 

e α (-)dφ/dt or e = -N * dφ/dt

where, N= number of turns in the coil. The negative sign indicates Lenz’s law.



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