, Chapter 8
Electromagnetic Waves
8.1 Introduction
• We will discuss about electromagnetic waves, their properties and characteristics, and also their practical
uses in our day-to-day life.
• One of the most important applications of electromagnetic waves is in communication.
• Some of the important applications of electromagnetic waves are:-
1. We are able to see everything around us because of electromagnetic waves.
2. It helps in aircraft navigation and helps the pilot for the smooth take-off and landing of aeroplanes. It
also helps to calculate the speed of the aeroplane.
3. In the medical field it has got very important applications. For example: - In laser eye surgery, in x-
rays.
4. In radio and television broadcasting signals. These signals are transmitted by electromagnetic waves.
5. Electromagnetic waves helps in determining the speed of the passing vehicles.
6. They are used in electronic appliances like T.V. remotes, remote cars, LED TV, microwave ovens etc.
7. Voice transmission in mobile phones is possible because of electromagnetic waves.
What are Electromagnetic Waves?
• Electromagnetic (EM) waves are the waves which are related to both electricity and magnetism.
• Electromagnetic (EM) waves are the waves which are coupled time varying electric and magnetic fields
that propagate in space.
• Waves associated with electricity and magnetism and as they are waves so they will propagate in the
space.
• When the electric and magnetic fields combine together and when they are varying with time they both
will give rise to electromagnetic waves.
• Electromagnetic equations emerged from Maxwell’s equations.
• Maxwell found these EM waves have so many special properties which can be used for many practical
purposes.
• Time varying electric field + Time varying magnetic field = Electromagnetic waves.
Maxwell’s Experiments
• Maxwell proposed that the time varying electric field can generate magnetic field.
, • Time varying magnetic field generates electric field (Faraday-Lenz law).
1. According to Faraday Lenz law an EMF is induced in the circuit whenever the amount of magnetic flux
linked with a circuit changes.
2. As a result electric current gets generated in the circuit which has an electric field associated with it.
According to Maxwell if Faraday’s law is true then the vice-versa should also be true, i.e. a time varying
electric field should also be able to generate a magnetic field.
Ampere’s Circuit Law:
• According to Ampere’s Circuital law, the line integral of magnetic field over the length element is equal to
μ0 times the total current passing through the surface ∫dl = μ0 l
• According to Maxwell there was some inconsistency in the Ampere’s circuital law.
• This means Ampere’s circuital law was correct for some cases but not correct for some.
• Maxwell took different scenarios i.e. he took a capacitor and tried to calculate magnetic field at a specific
point in a piece of a capacitor.
• Point P as shown in the figure is where he determined the value of B, assuming some current I is flowing
through the circuit.
• He considered 3 different amperial loops as shown in the figs.
• Ampere’s circuital law should be same for all the 3 setups.
Case 1: Considered a surface of radius r & dl is the circumference of the surface, then from Ampere’s
circuital law
𝑙 𝑜𝑟 𝐵 𝑙
𝜇𝑙
𝑜𝑟 𝐵
Case 2 : Considering a surface like a box & its lid is open and applying the Ampere’s circuital law
Electromagnetic Waves
8.1 Introduction
• We will discuss about electromagnetic waves, their properties and characteristics, and also their practical
uses in our day-to-day life.
• One of the most important applications of electromagnetic waves is in communication.
• Some of the important applications of electromagnetic waves are:-
1. We are able to see everything around us because of electromagnetic waves.
2. It helps in aircraft navigation and helps the pilot for the smooth take-off and landing of aeroplanes. It
also helps to calculate the speed of the aeroplane.
3. In the medical field it has got very important applications. For example: - In laser eye surgery, in x-
rays.
4. In radio and television broadcasting signals. These signals are transmitted by electromagnetic waves.
5. Electromagnetic waves helps in determining the speed of the passing vehicles.
6. They are used in electronic appliances like T.V. remotes, remote cars, LED TV, microwave ovens etc.
7. Voice transmission in mobile phones is possible because of electromagnetic waves.
What are Electromagnetic Waves?
• Electromagnetic (EM) waves are the waves which are related to both electricity and magnetism.
• Electromagnetic (EM) waves are the waves which are coupled time varying electric and magnetic fields
that propagate in space.
• Waves associated with electricity and magnetism and as they are waves so they will propagate in the
space.
• When the electric and magnetic fields combine together and when they are varying with time they both
will give rise to electromagnetic waves.
• Electromagnetic equations emerged from Maxwell’s equations.
• Maxwell found these EM waves have so many special properties which can be used for many practical
purposes.
• Time varying electric field + Time varying magnetic field = Electromagnetic waves.
Maxwell’s Experiments
• Maxwell proposed that the time varying electric field can generate magnetic field.
, • Time varying magnetic field generates electric field (Faraday-Lenz law).
1. According to Faraday Lenz law an EMF is induced in the circuit whenever the amount of magnetic flux
linked with a circuit changes.
2. As a result electric current gets generated in the circuit which has an electric field associated with it.
According to Maxwell if Faraday’s law is true then the vice-versa should also be true, i.e. a time varying
electric field should also be able to generate a magnetic field.
Ampere’s Circuit Law:
• According to Ampere’s Circuital law, the line integral of magnetic field over the length element is equal to
μ0 times the total current passing through the surface ∫dl = μ0 l
• According to Maxwell there was some inconsistency in the Ampere’s circuital law.
• This means Ampere’s circuital law was correct for some cases but not correct for some.
• Maxwell took different scenarios i.e. he took a capacitor and tried to calculate magnetic field at a specific
point in a piece of a capacitor.
• Point P as shown in the figure is where he determined the value of B, assuming some current I is flowing
through the circuit.
• He considered 3 different amperial loops as shown in the figs.
• Ampere’s circuital law should be same for all the 3 setups.
Case 1: Considered a surface of radius r & dl is the circumference of the surface, then from Ampere’s
circuital law
𝑙 𝑜𝑟 𝐵 𝑙
𝜇𝑙
𝑜𝑟 𝐵
Case 2 : Considering a surface like a box & its lid is open and applying the Ampere’s circuital law
