Lenz’s Law – Direction of induced e.m.f.

The direction of the e.m.f. induced in a conductor is such that it opposes the change producing it.

Solenoid (Right Hand Grip Rule)

A solenoid with a current flowing through it produces a magnetic field like that of a bar magnet. We can work out which end is the North Pole and which is the South by using the Right Hand Grip Rule from our force on a wire lesson. If our fingers follow the direction of the current through the coils our thumb points out of the North Pole.

*When we push the North Pole of a magnet the induced current in the solenoid flows to make a North Pole to repel the magnet.

*When we pull the North Pole out of the solenoid the induced current flows to make a South Pole to attract the magnet.

Fleming’s Right Hand Rule

If we are just moving a straight wire through a uniform magnetic field the direction of the induced current can be worked out using Fleming’s Right Hand Rule.

Your first finger points in the direction of the field from North to South, your thumb points in the direction the wire is moved and your middle finger points in the direction of the conventional current.