electromagnetic induction

electromagnetic induction

By Yohannes Kurnia

​The principles of electromagnetic induction:

The process of generating electricity from motion is called as electromagnetic induction.

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A coil of wire and a magnet, moving relative to each other are needed to induce a voltage across the ends of the wire.

When the coil and the magnetic field move relative to each other, a current flows through the coil if it is a part of a complete circuit. This is known as an induced current.

The actual reason why a current is induced is because the rotating coil cuts through the magnetic field lines.​

​When a wire is moved across a magnetic field, a small e.m.f. (voltage) is generated in the wire. The effect is called electromagnetic induction.

e.m.f. is an abbreviation for electromotive force.  When charge flows through a cell it is given energy by the cell.  The number of joules of energy given to each coulomb of charge that passes through the cell is the e.m.f. of the cell.

​E = q . V

​E = Energy (Joule)

q = numbers of charge that flow (Coulomb​)

V = e.m.f (Volt)​

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​Scientifically speaking, an e.m.f. is induced in the wire. If the wire forms part of a complete circuit, the e.m.f. makes a current flow. This can be detected by a meter called a galvanometer, which is sensitive to very- small currents.

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​Induced current direction: Fleming’s right-hand rule

If a straight wire (in a complete circuit) is moving at right angles to a magnetic field, the direction of the induced current can be found using Fleming’s right-hand rule, as shown below:

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​If the bar magnet is pushed into a coil of wire, an e.m.f. is induced in the coil.  If the magnet is withdrawn from the coil then an e.m.f. is induced in the opposite direction.

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​electromagnetic induction experiment: https://www.youtube.com/watch?v=hajIIGHPeuU​

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The induced e.m.f. (and current) can be increased by: 

(1) moving the magnet or wire faster; 

(2) using a stronger magnet; 

(3) increasing the turns on the coil.

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​The previous results are summed up by Faraday’s law of electromagnetic induction. In simplified form, this can be stated as follows:

The e.m.f. induced in a conductor is proportional to the rate at which magnetic field lines are cut by the conductor.

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Either of the following will reverse the direction of the induced e.m.f. and current:

§ moving the wire in the opposite direction

§ turning the magnet round so that the field direction is reversed.

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If the wire is not moving, or is moving parallel to the field lines, there is no induced e.m.f. or current.

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Multiple Choice

The basic requirement for inducing e.m.f. in a coil is that ………..

• flux should link the coil

• there should be change in flux linking the coil.

• coil should form a closed loop

• none of those

Multiple Choice

The diagram shows a bar magnet and a coil of wire. The bar magnet is moved at the same speed

in each experiment.

In which situation is the largest electromotive force (e.m.f.) induced?

Multiple Choice

A solenoid is connected in series with a sensitive ammeter. The N pole of a magnet is placed

next to one end of the solenoid, marked X.

First, the N pole of the magnet is pushed towards X, then the magnet is pulled away from X.

During both stages the ammeter deflects.

Which type of magnetic pole is induced at X during these two stages?

• as N pole moves

  towards X; X is N pole

  as N pole moves away

  from X; X is N pole

• as N pole moves

  towards X; X is N pole

  as N pole moves away

  from X; X is S pole

• as N pole moves

  towards X; X is S pole

  as N pole moves away

  from X; X is N pole

• as N pole moves

  towards X; X is S pole

  as N pole moves away

  from X; X is S pole