The induced e.m.f. has a polarity that, in a closed conducting circuit, drives a current whose magnetic effect opposes the change producing it.
Like magnetic poles repel and unlike poles attract. Viewed from one face of a current-carrying coil, anticlockwise current makes that face N; clockwise current makes it S.
North approaches: oppose the approach
As a north pole approaches a closed coil, the field through the coil changes. The induced current makes the near face north, so it repels the approaching north pole. Viewed from the magnet end, that current is anticlockwise.
North withdraws: oppose the separation
When the same north pole withdraws, the change is reversed. The coil's near face becomes south, attracting the magnet and opposing its withdrawal. Viewed from the same magnet end, the current is clockwise.
The induced effect opposes the change
Here the conducting loop is closed, so an induced current can flow. In each lower view, look from the magnet towards the loop. Brown shows current, teal shows the induced field, blue shows magnet motion and purple shows magnetic force on the magnet.
North approaches: near face becomes north
Repulsion opposes the approach. The induced field points out of the near face.
North withdraws: near face becomes south
Attraction opposes the separation. The induced field points into the near face.
South approaches: near face becomes south
Repulsion opposes the approach. The induced field points into the near face.
South withdraws: near face becomes north
Attraction opposes the separation. The induced field points out of the near face.
For a north pole, approach produces a near N face and withdrawal a near S face. The current directions are viewed from the magnet side. The response opposes the motion that changes the field through the coil.
Closed coil, viewed from the magnet end.
Magnet motion
Near coil face
Current in that face view
N approaches
N: repels
Anticlockwise
N withdraws
S: attracts
Clockwise
S approaches
S: repels
Clockwise
S withdraws
N: attracts
Anticlockwise
Predict a new case
A south pole moves away
First identify the change: the magnet and coil are separating. To oppose that separation, the near coil face must attract the south pole, so it becomes north.
A north face requires anticlockwise current when viewed from the magnet end. Work from the change to the pole, then from the pole to the current direction.
The induced field does not always oppose the magnet's original field. During withdrawal, it acts to maintain a field that is decreasing. The rule concerns opposition to the change.
Where does the electrical energy come from?
When the induced current supplies a load, work is needed to keep moving the magnet or coil against the opposing magnetic effect. That external work provides the electrical output and any heating losses.
The opposing effect need not prevent the motion: an external force can maintain it while doing work. The magnet is not steadily consumed as fuel. In a generator, the mechanical energy source must keep turning the rotor.
Optional check A north pole is withdrawn from a closed conducting coil. Viewed from the magnet end, which induced pole and current direction oppose that withdrawal?