Magnetism- physics

• Differences between a permanent magnet and an induced magnet

  • A permanent magnet produces its own magnetic field
  • An induced magnet becomes magnetic when placed in a magnetic field
• When an induced magnet is removed from a magnetic field, it loses most/all of its magnetism
• Examples of magnetic materials

  • Iron
  • Steel
  • Cobalt
  • Nickel
• What happens when an induced magnet is removed from a magnetic field

  The induced magnet loses most/all of its magnetism
• The magnetic field strength decreases the further you move away
• Direction of a magnetic field

  • In the direction that a north pole would experience a force if placed in the field
  • From the north seeking pole to the south seeking pole of a magnet
• Magnetic field

  The region surrounding a magnet where another magnet or magnetic material experiences a non-contact force
• A magnetic field is produced around the wire
• Factors determining the strength of the magnetic field around a current-carrying wire

  • The magnitude of the current flowing through the wire
  • The distance from the wire
• A solenoid is a coil of wire which, when current passes through, creates a strong magnetic field
• The rule used to determine the force experienced due to the motor effect is Fleming’s Left-Hand Rule
• The magnetic field found inside a solenoid is strong and uniform
• Characteristics of an electromagnet

  • A solenoid with an added iron core
  • Adding the iron core increases the strength of the magnetic field
• The motor effect is when a force is exerted between a magnetic field and a current-carrying conductor placed in that field
• Factors affecting the size of the force on a current-carrying wire in a magnetic field

  • The magnitude of the current flowing through the conductor
  • The strength of the magnetic field that the conductor is placed in
• Fleming’s Left-Hand Rule

  1. Forefinger represents the direction of the magnetic field

  2. Second finger represents the direction of current flow in the conductor
• Criteria for the equation linking force, magnetic flux density, current, and length to hold
• If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased

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

  The direction of the force is reversed
• How an electric motor works

  1. A coil of wire, carrying a current, is placed in a magnetic field

  2. The forces on the two sides perpendicular to the field experience forces in opposite directions

  3. This causes a rotational effect
• How a loudspeaker works

  1. A cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field

  2. When current flows through the wire, it creates a second magnetic field, which interacts with the permanent field

  3. This produces a force which causes the cone to vibrate
• How the pitch of the sound from a loudspeaker is changed

  1. The frequency of the a.c current is altered

  2. This creates a different frequency of vibration in the cone
• The conductor must be at right-angles to the magnetic field it is placed in
• Unit used for magnetic flux density is Tesla, T
• Loudspeakers make use of the motor effect to convert variations in the current of an electrical circuit into pressure variations which produce audible sound
• A potential difference is induced across the ends of the conductor
• The conductor must form a closed loop or be part of a complete circuit
• Electromagnetic effect used by a microphone

  • The generator effect
  • The microphone takes advantage of the generator effect
• Ways to generate different types of current using the generator effect

  • In an alternator to produce alternating current
  • In a dynamo to produce direct current
• The direction of the field is such that it opposes the change that induced the current. This change is either the movement of the conductor or a change to the field
• The current flowing through the primary coil of a transformer must be alternating because
• Makeup of a basic transformer

  • Primary coil
  • Secondary coil of wire wrapped around an iron core
• Iron is used as the core for a transformer because it is easily magnetised
• 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 to flow in the secondary coil
• Electromagnetic effect a microphone takes advantage of

  1. The generator effect

  2. It converts the pressure variations in sound waves into alternating current in a circuit
• About the electrical power input and output of a 100% efficient transformer