The Motor Effect

• What is produced when current flows through a conducting wire?

  A magnetic field is produced around the wire
• What determines the strength of the magnetic field around a current-carrying wire?

  The magnitude of the current and distance from the wire
• Describe the magnetic field found inside a solenoid.

  Strong and uniform
• How does adding an iron core affect the magnetic field strength of an electromagnet?

  It increases the strength of the magnetic field
• What is the motor effect?

  A force between a magnetic field and a current-carrying conductor
• When using Fleming’s left hand rule, what does the forefinger represent?

  The direction of the magnetic field
• When using Fleming’s left hand rule, what does the second finger represent?

  The direction of current flow in the conductor
• What factors affect the size of the force on a current-carrying wire in a magnetic field?

  The magnitude of the current and strength of the magnetic field
• If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force?

  The direction of the force is reversed
• If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force?

  The strength of the force is increased
• What criteria must be met for the equation linking force, magnetic flux density, current and length to hold?

  The conductor must be at right-angles to the magnetic field
• What is the unit used for magnetic flux density?

  Tesla, T
• How does an electric motor work?

  A coil in a magnetic field experiences forces causing rotation
• How do loudspeakers make use of the motor effect?

  They convert current variations into sound pressure variations
• Explain how a loudspeaker works.

  A cone with wire vibrates in a magnetic field
• How is the pitch of the sound from a loudspeaker changed?

  By altering the frequency of the a.c current