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What is Electromagnetic Induction?

Principles and Worked Examples


Electromagnetic (EM) induction occurs when an electromagnetic field (emf) is induced in a wire, or more precisely when a complete loop of wire cuts across lines of a magnetic field; the movement induces a current and therefore an emf.


The emf can be increased by moving the wire faster, using a stronger magnet and making wires into a coil and ensuring that the wires cut across the field at 90 degrees.


The direction of the current induced is dependant on the direction of the magnetic field.


A current carrying wire






We can determine the direction of the field using the Right hand 'screw' rule for B field around a current carrying wire. The thumb represents the direction of the current and the fingers curve to follow the direction of the magnetic field.








A Solenoid

Solenoid Poles

The poles of a solenoid can be determined using the right hand screw rule and knowing that field lines always come out of the north pole and into the south.

Magnetic field





When drawing the magnetic field lines around a solenoid the crosses represent wires going into the page and the dots out of the page.