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A to Z of Electromagnetic Induction for IIT JEE !

Electromagnetic InductionElectromagnetic Induction was first discovered way back in the 1830’s by Michael Faraday. Faraday noticed that when he moved a permanent magnet in and out of a coil or a single loop of wire it induced an Electromotive Force or EMF. In other words a voltage, and therefore a current were produced. So what Michael Faraday discovered was a way of producing an electrical current in a circuit by using only the force of a magnetic field and not batteries. This then lead to a very important law linking electricity with magnetism, Faraday’s Law of Electromagnetic Induction. 

The various topics that form a part of electromagnetic induction include:

  • Faraday’s Laws of Electromagnetic InductionBiography of Michael Faraday

  • ?Lenz’s Law

  • Motion of a loop in a uniform magnetic field

  • Self-induction and co-efficient of self-induction

  • Mutual-induction 

  • Co-efficient of mutual-induction

  • Energy stored in an inductor

  • Fleming’s right and left hand rule

  • Eddy current

  • Alternating current

  • Coil rotating in a uniform magnetic field   

We shall give a brief outline of these topics in addition to the tips to master them. Those willing to go into the intricacies can refer the study material page on electromagnetic induction.                                                    

Important Formulas 

Magnetic Flux

        FB = BA cos ?

Induced Electric Potential

        e = -??B/?t

Energy Stored in a Magnetic Field

        Umag = (½ µ0) B2

Time Constant for an RL Circuit

        I = V/R (1-e-t/t)

Energy Stored in an Inductor

        Uind = (½)LI2


Is this a valuable topic for those who are preparing for IIT-JEE, NEET (AIPMT) and CBSE Exam?

Electromagnetic induction is one of the easiest topics in physics, and one can easily score good marks in it. It is foolish to leave the questions from this section. Moderate levels of questions are coming from this section. The electromagnetic induction part contributes almost 5% in the IIT-JEE and the other two exams. 

What are the best books for the preparation of electromagnetic induction?

Some of the books which are considered to be best for preparation of this section are:

Problems of varied complexities can be found in the book Resnick Halliday. It has also a special edition dedicated to IIT-JEE. The standard of Irodov physics is quite high. At the end, H.C. Verma is quite useful for these examinations.


Question 1:- [IIT JEE 2014]

Two ideal batteries of emf V1 and V2 and three resistances R1, R2 and R3 areconnected as shown in the figure. The current in resistance R2 would be zero if                   

  A.V1 = V2 and R1 = R2 = R3?            B.V1 = V2 and R1 = 2R2 = R3

  C.V1 = 2V2 and 2R1 = 2R2 = R3      D.2V1 = V2 and 2R1 = R2 = R3


Current through R2 will be zero of Eeqv of two batteries is zero

So, (V1/R1 – V2/R3)/(1/R1 + 1/R3) = 0 Or, V1/R1 = V2/R3

In option (A), V1 = V2 that gives, R1 = R3 whatever be the value

of R2 to maintain image of loop V1 with respect to V2.

Hence, option A and B both are correct.In options, C and D,

using loop analysis method we find,V1/V2 = 2, that satisfied, R3/R1 = 2

This relation is satisfied by option A &B.Hence, A, B and C are correct.


Question 2:- [JEE Advanced 2013]

A point Q is moving in a circular orbit of radius R in the x-y plane with angular velocity ω. This can be considered as equivalent to a loop carrying a steady current Qω/2π. A uniform magnetic field along the positive z-axis is now switched on, which increases at a constant rate from 0 to B in one second. Assume that the radius of the orbit remains constant. The application of the magnetic field induces an emf in the orbit. The magnitude of the induced electric field in the orbit at any instant of time during the time interval of the magnetic field change, is

A.BR/4        B.BR/2        C.BR        D.2BR


E (2πR) = πR2 (dB/dt)
So, E = RB/2
So the option (B) is correct.


Some Interesting Facts

  • Electromagnetic induction is the production of an electromotive (emf) in a conductor as a result of a changing magnetic field about the conductor.

  • The induced emf is always such that it opposes the change that gives rise to it, according to Lenz's law.

  • Changing the current in a given circuit can also induce an emf in another, nearby circuit unconnected with the original circuit; this type of electromagnetic induction, called mutual induction, is the basis of the transformer.

  • Electrostatic induction is the production of an unbalanced electric charge on an uncharged metallic body.

  • Magnetic induction is the production of a magnetic field in a piece of unmagnetized iron or other ferromagnetic substance when a magnet is brought near it.

Tips to Study Electromagnetic Induction

Electromagnetic induction is one of the important chapter for the IIT-JEE aspirant’s. Often students doing mistake due to the lack of concept regarding the direction of electric- magnetic field and induced emf. Below are the some useful tips to handle this topic so quickly and accurately. 
  • Always three parameters are involved in an electromagnetic induction problem. One is magnetic field, second one is a inductor or coil and the third one is movement of coil with respect to field.

  • Basically, in a given problem, two quantities are known and the third quantity needs to be calculated.

  • Before attempting the problem, check the units of all the parameters must belong to any one standard unit system. That is either in S.I or C.G.S.

  • Must aware of the Generator Rule which is the principle to determine the direction of induced emf of a conductor moving in a magnetic field. 

  • Know the proper law and some concept regarding the direction of electric and magnetic field.

  • Clear your concept by doing the more and more problem on application of Faraday’s law, Lenz’s law, Fleming’s right hand and left hand thumb rule for current.

  • Since problems are directly coming from this section by using formulae and little concept, so try to save your time for difficult section like mechanics

Practical Applications of Electromagnetic Induction

  • Some electric generators can be driven by human power such as a hand crank or a motor car to generate electricity by the principle of electromagnetic induction.

  • A transformer uses two important connections between electricity and magnetism to convey power from one AC circuit to another results the application of electromagnetic induction.

  • An electric generator which a device for transforming mechanical energy to electrical energy to generate electricity is one of the applications of electromagnetic induction. 

  • The bulb in the halogen desk lamp operates from low voltages provided with the help of a transformer, which based on the theory of electromagnetic induction.

  • A hybrid automobile couples together a combustion engine and one or more motor/generators so that it can convert energy easily between mechanical and electric forms and can operate on fuel, battery, or both by the help of electromagnetic induction principle.

  • Loudspeakers use electromagnets to vibrate the cone and produce sound based on the principle electromagnetic induction.

  • Using electromagnetic induction, powerful magnets can be turned on and off using electricity, unlike permanent magnets.

  • Radio’s, televisions, refrigerators are all contains transformers resulting uses of electromagnetic induction principle.

  • The ignition system of a car as well as starter are based on the theory of electromagnetic induction

  • In a commercial electric power plant, large generators produce energy that is transferred out of the plant by electric transmission. These generators use magnetic induction to generate a potential difference when coils of wire in the generator are rotated in a magnetic field.

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