Class 12 Physics Electromagnetic Waves Maxwells Experiments

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 amagnetic field.
• 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

∫ B.dl = μ0 l

or B(2πr) = μ0 l

or B = μ0 l  / 2πr

Case 2 : Considering a surface like a box & its lid is open and applying the Ampere’s circuital law

∫ B.dl = μ0 l

As there is no current flowing inside the capacitr, therefore I = 0

Or ∫ B.dl = 0

Case 3: Considering the surface between 2 plates of the capacitor, in this case also I=0, so B=0

• At the same point but with different amperial surfaces the value of magnetic field is not same.They are different for the same point.
• Maxwell suggested that there are some gaps in the Ampere’s circuital law.
• He corrected the Ampere’s circuital law. And he made Ampere’s circuital law consistent in all the scenarios.

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