4.2.3 motor effect 2

• The catapult experiment

  • The catapult experiment shows that a wire carrying a current in a magnetic field experiences a force.
  • When the power supply is switched on, a current flows in the free wire and so this wire feels a force which causes it to move.
  • Swapping the north and south poles of the magnet will reverse the wire’s direction of movement.
  • Swapping the wires connecting to the power supply reverses the direction of the current.
  • Reversing the direction of the current will reverse the direction that the wire moves.
• The catapult experiment shows that a wire carrying a current in a magnetic field experiences a force.
• The force on a wire in a magnetic field is directly proportional to the length of the wire in the magnetic field
• The force on a wire in a magnetic field is directly proportional to the current through the wire
• The force on a wire in a magnetic field is directly proportional to the strength of the magnetic field
• force = magnetic flux density * current * length

  • F=BIL
• In a magnetic field, a coil of wire carrying a current experiences forces that make it rotate about its axis. The size of the turning force acting on the coil can be increased in three ways.

  • increasing the current through the coil
  • increasing the magnetic field strength
  • increasing the number of turns on the coil
• Increasing the number of turns on the coil

  • increases the size of the turning force
• Increasing the magnetic field strength

  • increases the size of the turning force
• Increasing the current through the coil

  • increases the size of the turning force
• What are the units for magnetic flux density?

  Tesla