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Induced EMF via motion of conductor

Physics (Year 12) - Electro-magnetism

Dev Lohar

Electromagnetic induction

When a conductor moves perpendicular through a magnetic field, then an electric current will begin to flow inside that conductor. This creation of electric current is called electromagnetic induction and the generated electric current is sometimes referred to as the induced emf.

You can think of it as the opposite of how an electric current moving through a conductor generates a magnetic field around it. If there was no electric current, then there won’t be any magnetic field. So the opposite of that would be a conductor moving perpendicular through a magnetic field and due to that motion it generates an electric current. If the conductor isn’t moving, then there won’t be any electric current.

It is also important to note the motion of the conductor; perpendicular through a magnetic field. If a conductor is moving parallel to a magnetic field, then no current would be generated. You could also think of it as the conductor needs to cut through the magnetic field lines (i.e. cut through magnetic flux). If it’s not cutting through the lines, then no emf is generated.


The magnitude of the induced emf can be found by the following equation:

If v and B are not perpendicular then the component of B which is perpendicular to direction of the moving conductor needs to be used. This can be done by:


Direction of induced emf

To find the direction of the induced current, we use a slightly modified version of the right hand palm rule. The modification being that instead of our right hand, we use our left hand. Everything else stays the same; direction of the fingers represents the direction of the magnetic field, direction of the thumb represents the direction of the electric current and direction of the palm represents direction of the force.

To find the direction of the induced emf, use your left hand and point your fingers in the direction of the magnetic field and your palm in the direction which the conductor is moving. The direction your thumb points at will be the direction of the induced emf through the conductor.


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