Electromagnetic

• Which parts of a magnet are the magnetic forces the strongest?

  Poles of the magnet
• What happens when two magnets are brought close to each other?

  They exert a force on each other

  Like poles = a repulsive, non- contact force

  Unlike poles = an attractive, non-contact force
• Difference between permanent and induced magnet?

  • Permanent magnet produces its own magnetic field
  • An induced magnet becomes magnetic when placed in a magnetic field
• What type of force does induced magnetism always cause?

  A force of attraction
• What happens when an induced magnet is removed form a magnetic field ?

  Induced magnet loses most/all of its magnetism
• What is a magnetic field?

  The region surrounding a magnet eher another magnet or magnetic material experiences a non-contact force
• Four examples of magnetic materials

  1. Iron
  2. steel
  3. cobalt
  4. nickel
• How does the strength of a magnetic field alter as you move further away from the magnet producing it?

  The magnetic field strength decreases the further you move away
• In what direction does a magnetic field point?

  • In the direction that a North Pole would experience a force if placed in the field
  • Form the north seeking pole to the south seeking pole
• What does a magnetic compass contain?

  A small bar magnet that points in the direction of the earths magnetic field
• 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?

  • Magnitude of the current flowing through the wire
  • The distance from the wire
• What is a solenoid?

  A coil of wire which when current passes through creates a strong magnetic field
• Describe the magnetic field found inside a solenoid

  Strong and uniform
• What is electromagnet?

  • A solenoid with an added iron core
  • Adding the iron core increases the strength of the magnetic field
• 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
• What is the motor effect?

  A force between a magnetic field and a conductor
• What rule is used to determine the force experienced due to the motor effect?

  Fleming’s Left-Hand Rule
• In Fleming’s left hand rule, what does the forefinger represent?

  The direction of the magnetic field
• In 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 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 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 of wire carries a current
  • It is placed in a magnetic field
  • Forces on two sides perpendicular to the field act in opposite directions
  • This causes a rotational effect
• How do loudspeakers make use of the motor effect?

  • Converts variations in current of an electrical circuit
  • Produces pressure variations that create audible sound
• Explain how a loudspeaker works.

  • A cone with wire is connected to an a.c power supply
  • It is placed in a permanent magnetic field
  • Current through the wire creates a second magnetic field
  • Interaction produces a force causing the cone to vibrate
• How is the pitch of the sound from a loudspeaker changed?

  • The frequency of the a.c current is altered
  • This creates a different frequency of vibration in the cone
• What happens when an electrical conductor moves relative to a magnetic field?

  A potential difference is induced across the conductor
• What happens to an electrical conductor when there is a change to the magnetic field?

  A potential difference is induced across the conductor
• What is required for an induced potential difference to cause current flow?

  The conductor must form a closed loop
• What can be said about the direction of the magnetic field produced by an induced current?

  It opposes the change that induced the current
• What are two ways the generator effect is used to generate different types of current?

  • In an alternator to produce alternating-current
  • In a dynamo to produce direct-current
• What is the makeup of a basic transformer?

  A primary coil and a secondary coil
• What electromagnetic effect does a microphone take advantage of?

  The generator effect
• How does a microphone convert sound waves?

  It converts pressure variations into alternating current
• Why is iron used as the core for a transformer?

  It is easily magnetised
• Explain how a transformer works.

  1. An alternating current flows through the primary coil
  2. This induces a changing magnetic field in the core
  3. This changing magnetic field induces a current in the secondary coil