1. 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.

2. The Motor effect

3. The Motor effect

4. The Motor effect
The force is increased
by increasing the:

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

6. 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.

10. 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

11. 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

12. 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

13. 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

14. For a faster spin?

15. 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

16. 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

17. 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:

18. 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

19. 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

20. 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:

21. 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

22. 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

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

24. 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 !! )

25. 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?