The Motor Principle

An electromagnet that interacts with another magnet can create a directed force (as discovered by Faraday as the first motor).

Use LHR for motors:Fingers point in the direction of the magnetic field lines (that travel from N to S), thumb points in the direction of negative current flow, the palm of hand indicates the direction of the force that is produced (note that this force is perpendicular to current flow which is perpendicular to magnetic field lines).

• The production of this force along with the use of a commutator (which reverses current flow) produces a polarity change in the magnetic field. This reversal creates another force in the same direction as the first force, and continues the rotating pattern of the motor. See page 568 in textbook.

Armature Motor

Electromagnetic Induction – Lenz`s LawIf moving electrons in a conductor causes a magnetic field to be created, then it makes sense that a magnetic field that changes in intensity near a conductor would cause electrons to move.

Putting a magnet into a wire coil causes electrons to flow in one direction while moving a magnet out of a wire coil causes electrons to flow in the opposite direction.

Lenz’s Law states that the direction of induced current flow creates an induced magnetic field that opposes the motion of the inducing magnet.

In simple terms:1) When pulling a magnet out of a coil, the magnetic poles are opposite (opposes the motion).2) When putting a magnet into a coil, the magnetic poles are similar (opposes the motion by repelling).

LHR for Lenz’s Law• Same rule as for coiled conductors:Fingers curl in the direction of negative current flow, thumb points toward the N end of the magnetic field. *the inducing magnet will be opposing the magnetic field of the coil.