The motor effect

What conditions are needed for the motor effect?

• current carrying wire produces a magnetic field around it

• The wire is placed into the magnetic field of a permanent magnet

• The magnetic fields interact

• The wire experiences a force

Factors affecting size of the force:

• increasing current through the wire

• Use a stronger permanent magnet

• Placing the wire at 90 degrees to the direction of the permanent magnet field lines

In FLHR what goes the thumb represent?

Motion / force

In FLHR what does the first finger represent?

Direction of the magnetic field

In FLHR what does the second finger represent?

The current

What is the purpose of brushes and commutator in a DC motor?

• provide a connection from power supply to the coil

• Reverses the direction of the current in the child every half turn

• This reverses the direction of the magnetic field in the coil

• The force is in the same direction

• The motor turns the same way

Describe how a motor works:

• There is a current in the coil

• This induces a magnetic field around the coil

• The magnetic field of the wire and the permanent magnets interact

• There is a force on the wire dictated by Flemming’s left hand rule

• This means that the force on each side of the coil is in opposite directions

• The split ring commutator reverses the direction of the current each half turn so the force is in the same direction and the motor turns in the same direction.

Describe how a loudspeaker works:

• The current on the wire is varying

• This produces a magnetic field which also varies

• The varying magnetic field interacts with the magnetic field of the permanent magnets

• This produces a force on the coil which is varying

• This varying force vibrates the cone

• This vibrates the surrounding air particles which produces a longitudinal sound wave