Electromagnetic Preparation Tips for IIT JEE | askIITians

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Electromagnetic Induction
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Electromagnetic Induction for IIT JEE !

• Electromagnetic Induction was first discovered
  way back in the 1830s 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,
  Faradays Law of Electromagnetic Induction.

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The various topics that form a part of
electromagnetic induction include

• Faradays Laws of Electromagnetic Induction
• Lenzs 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
• Flemings 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.
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Important Formulas
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Is this a valuable topic for those who are
preparing for IIT-JEE, 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
• Resnick Halliday
• I.E. Irodov
• H.C Verma
• 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.

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Illustrations

• Question 1- IIT JEE 2014
• Two ideal batteries of emf V1 and V2 and
  three resistances R1, R2 and R3 are connected 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
• Solution-
• 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.

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• 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
  ?. This can be considered as equivalent to a loop
  carrying a steady current Q?/2p. 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
• Solution-
• E (2pR) pR2 (dB/dt) So, E RB/2 So
  the option (B) is correct.

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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.

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Tips to Study Electromagnetic Induction

• Electromagnetic induction is one of the
  important chapter for the IIT-JEE aspirants.
  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 Faradays law, Lenzs
  law, Flemings right hand and left hand thumb
  rule for current.

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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.

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