electromagnetism

• what are magnetic field lines created by?

  a current. The magnetic field lines are circles around a single conducting wire.
• what does the strength of a magnetic field depend on?

  • the size of the current
  • the distance from the wire
• what is the right hand grip?

  the direction of the field lines depend on the direction of the current.

  • grip the wire with your right hand, with the thumb pointing in the direction of the current.
  • your fingers curled around the wire will point in the direction of the magnetic field.
• what are the field lines like inside the coil?

  closely spaced parallel lines.
• what do the magnetic fields of individual coils of wire add up to create?

  a strong, uniform magnetic field in the coil.
• what is a solenoid?

  a loop of wire coiled into a cylindrical shape.
• what do field lines look like outside of a solenoid?

  like the field lines around a bar magnet, with a clear north and south pole. The magnetic field is weaker outside of a solenoid.
• with solenoids, where is the magnetic field strongest?

  inside the solenoid.
• what is the magnetic field like inide of solenoid?

  strong and uniform
• what is the magnetic field like outside of the coil of wire?

  the magnetuc field decreases in strength the further away it is from the solenoid.
• for a straight wire carrying a current, where is the magnetic field the strongest?

  at the points closest to the wire.
• for a straight wire carrying a current, where is the magnetic field the weakest?

  further away from the wire.
• for both solenoids and straight wires, increasing the size of the current increases the strength of the magnetic field.
• for both solenoids and straight wires, flipping the direction of the current flips the direction of the magnetic field lines.
• what happens when a wire with a current flowing through it is placed in a magnetic field?

  the magnet and the conductor will experience a force due to the motor effect.
• the field created by an electric current interacts with the magnetic field that the wire is placed inside. This causes a force on the wire.
• what does the direction of the force on a wire depend on?

  the direction of the magnetic field and the direction of the current flow. (Flemming's Left hand rule).
• what is Flemming's left hand rule?

  • first finger: direction of magnetic field (First = field).
  • second finger: direction of current (seCond = current).
  • thumb: direction of force/direction conductor would move (thuMb = motion).
• what does the catapult experiment show?

  that a wire carrying a current in a magnetic field experiences force.
• what is the catapult experiment?

  • when the power supply is switched on, a current flows free in the wire, the wire feels a force, causing 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 reverse the direction of the current.
  • reversing the direction of the current will reverse the direction that the wire moves.
• what is the force on a wire in a magnetic field directly proportional to?

  • the strength of the magnetic field
  • the current flowing through the wire
  • the length of the wire in the magnetic field
• what is the equation for the force on a current carrying wire?

  force = magnetic field strength x current x length of wire
• what does the force on a wire in a magnetic field depend on?

  • magnetic field strength
  • current
  • length of wire
• why will a coil carrying an electric current rotate in a magnetic field?

  because the current going up one side of the coil is flowing in the opposite direction to the current coming back down the other side. Using fleming's left hand rule, we see that one side of the coil will move downwards and the other side of the coil will move upwards.
• what effect does increasing the force acting on the coil in a DC motor have?

  • more turns on the coil
  • stronger magnetic field
  • higher current through the coil
• magnetic field strength is also known as what?

  magnetic flux density
• what does a split ring commutator do?

  reverses the direction of the current every half-turn of the coil. This ensures that the current is always moving in the right direction to keep the coil rotating.
• in a magnetic field, a coil of wire carrying a current experiences a force that will make it what?

  rotate about its axis.
• in what 3 ways can the size of the turning force acting on the coil be increased?

  • increasing the number of turns on the coil
  • increasing the current through the coil
  • increasing the strength of the magnetic field
• a change in current causes a change in magnetic field.
• as the direction of the current changes, the direction of the magnetic field induced in the electromagnet changes.
• a stationary magnet repeatedly attracts and repels the electromagnet.
• how are sound waves created in a loud speaker?

  • as the direction of the current changes, the direction of the magnetic field induced in the electromagnet changes.
  • a stationary magnet repeatedly attracts and repels the electromagnet.
  • This causes the speakers the move backwards and forwards which creates soundwaves.
• in what form is the signal passed to the loudspeaker?

  changing current.
• what is converted to sound waves by a speaker?

  Electrical signals
• a moving-coil loudspeaker or set of headphones has what inside a coil?

  an electromagnet