The Motor effect Learning Outcomes Most students should be able to: • Describe the effect of increasing the current or magnetic field strength on a current carrying wire. • Describe how an electric motor and loudspeaker work Some students should also be able to: • Describe and explain the effect of making changes to the design or operation of an electric motor. Key points The students should be able to draw a diagram showing the effect of a magnetic field on a current carrying wire including the direction of the force.

The Motor effect

The Motor effect

The Motor effect The force is increased by increasing the:

The Motor effect The force is increased by increasing the: Current Magnetic strength

The Motor effect The force is increased by increasing the: Current Magnetic strength The force is decreased to zero by making the angle of the wire become parallel to the field lines.

A magnetic field circulates around a wire Current into page N O R T H S O U T H X A magnetic field circulates around a wire N O R T H S O U T H X Force

Current into page N O R T H S O U T H X N O R T H S O U T H X Force

A magnetic field circulates around a wire Current into page N O R T H S O U T H X A magnetic field circulates around a wire N O R T H S O U T H X Force

N O R T H S O U T H X N O R T H S O U T H X Force The motor effect Current into page N O R T H S O U T H X A magnetic field circulates around a wire N O R T H S O U T H The motor effect - showing resultant field X Force

For a faster spin?

For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps

For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps

The motor spins when a current is passed through the coil because: For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps The motor spins when a current is passed through the coil because:

The motor spins when a current is passed through the coil because: For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps The motor spins when a current is passed through the coil because: a force acts on each side of the coil – due to the motor effect

The motor spins when a current is passed through the coil because: For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps The motor spins when a current is passed through the coil because: a force acts on each side of the coil – due to the motor effect the forces on each side act in opposite directions

The motor spins when a current is passed through the coil because: For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps The motor spins when a current is passed through the coil because: a force acts on each side of the coil – due to the motor effect the forces on each side act in opposite directions The commutator reverses the current in the coil every half turn because:

The motor spins when a current is passed through the coil because: For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps The motor spins when a current is passed through the coil because: a force acts on each side of the coil – due to the motor effect the forces on each side act in opposite directions The commutator reverses the current in the coil every half turn because: the sides swap over each half turn

The motor spins when a current is passed through the coil because: For a faster spin? Use: Higher current Stronger magnets More turns on the coil Use a soft iron core curved pole pieces reducing air gaps The motor spins when a current is passed through the coil because: a force acts on each side of the coil – due to the motor effect the forces on each side act in opposite directions The commutator reverses the current in the coil every half turn because: the sides swap over each half turn then the coil is pushed in the same direction every half turn

The Loud speaker The loudspeaker cone moves outwards then inwards because:

The Loud speaker The loudspeaker cone moves outwards then inwards because: of the motor effect between a current carrying coil in a permanent magnetic field. ( strong !! )

Why does a cone not produce sound The Loud speaker The loudspeaker cone moves outwards then inwards because: of the motor effect between a current carrying coil in a permanent magnetic field. ( strong !! ) The input signal is ac with a range of frequencies. Each time the current changes direction the force changes direction so the cone vibrates Why does a cone not produce sound when a direct current is passed through it?