P7: The Motor Effect Physics GCSE

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

  A magnetic field
• How can the shape and direction of the magnetic field around a wire be investigated?

  Using plotting compasses
• What does the magnetic field around a current-carrying wire look like?

  • Made up of concentric circles
  • Indicates no poles
  • Circles get further apart with distance
• What does the right-hand thumb rule help determine?

  The direction of current and magnetic field
• What happens to the direction of the magnetic field when the current direction is reversed?

  The direction of the magnetic field reverses
• What occurs if there is no current flowing through the conductor?

  No magnetic field is produced
• How does increasing the current affect the magnetic field strength around a wire?

  It increases the strength of the magnetic field
• What is the magnetic field pattern around a solenoid?

  • Magnetic field lines circle around the coil
  • Similar to that of a bar magnet
  • Strong and uniform inside the solenoid
• How can the strength of the magnetic field around a solenoid be increased?

  By coiling the wire to form a solenoid
• What does one end of a solenoid behave like?

  The north pole of a magnet
• How can you determine the polarity of each end of a solenoid?

  By viewing it from the end
• What indicates that the current is flowing clockwise in a solenoid?

  It is the south pole
• What happens to the poles of a solenoid if the current changes direction?

  The north and south poles will reverse
• How can the strength of the magnetic field around a solenoid be increased?

  • Increase the current flowing through the wire
  • Increase the number of turns in the coil
  • Reduce the length of the wire while maintaining turns
  • Add an iron core through the coils
• What is an electromagnet?

  A solenoid with an iron core
• What happens to the magnetic field of an electromagnet when the current is switched off?

  No magnetic field is produced
• How can the strength of an electromagnet be changed?

  By increasing or decreasing the current
• What happens when the electromagnet in a scrapyard crane is switched on?

  It attracts magnetic materials
• What occurs when the electromagnet in a scrapyard crane is switched off?

  It drops the magnetic materials
• How does an electric bell operate?

  1. Button pressed, current flows through electromagnet
  2. Magnetic field attracts iron armature
  3. Hammer strikes the bell
  4. Armature movement breaks the circuit
  5. Current stops, magnetic field disappears
  6. Armature returns, circuit re-establishes
• What is the motor effect?

  A force on a wire in a magnetic field
• What causes the motor effect?

  Two interacting magnetic fields
• What happens when a wire with current is placed in a magnetic field?

  It experiences a force
• What factors can increase the force exerted by magnetic fields on a wire?

  • Increase the current flowing through the wire
  • Use stronger magnets
  • Place the wire at 90° to the magnetic field
• What is the equation to calculate the force on a current-carrying wire?

  F = BIL
• What do the variables in the equation F = BIL represent?

  F = force, B = magnetic flux density, I = current, L = length
• If a 5 cm length of wire carries a current of 1.5 A and experiences a force of 0.06 N, how do you calculate the magnetic flux density?

  Use F = BIL to find B
• What is the maximum force on a wire in a magnetic field?

  When the wire and field are perpendicular
• What does Fleming's Left-Hand Rule help determine?

  The direction of force, magnetic field, and current
• What are the steps to use Fleming's Left-Hand Rule?

  1. Point First Finger in direction of magnetic field
  2. Rotate hand so Second Finger points in direction of current
  3. Thumb points in direction of thrust (force)
• How does a simple d.c. motor operate?

  • Coil of wire rotates in a magnetic field
  • Current flows through the coil
  • Forces act in opposite directions on the coil
  • Split ring maintains current flow
• What happens when the coil in a d.c. motor rotates 90°?

  No current flows, no forces act
• What continues the rotation of the coil in a d.c. motor?

  The momentum of the coil
• What factors can increase the speed of a d.c. motor?

  • Increase the current
  • Use a stronger magnet
• How can the direction of rotation in a d.c. motor be changed?

  • Reverse the direction of the current supply
  • Reverse the direction of the magnetic field
• How can the force supplied by a d.c. motor be increased?

  • Increase the current in the coil
  • Increase the strength of the magnetic field
  • Add more turns to the coil
• What should you do to determine the direction of rotation in a d.c. motor?

  Use Fleming's Left Hand Rule
• What does the term 'split-ring commutator' refer to?

  A split ring in the circuit