Magnetism and electromagnetism

• What type of force does induced magnetism always cause?

  A force of attraction
• Examples of magnetic materials:

  Iron

  Steel

  Cobalt

  Nickel
• In what direction does a magnetic field point?

  > 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
• 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 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
• What is an electromagnet?

  > A solenoid with an added iron core

  > Adding the iron core increases the strength if the magnetic field
• What is the motor effect?

  When a force is exerted between a magnetic field and a current carrying conductor placed in that field
• What is the rule used to determine the force experienced due to the motor effect?

  Fleming’s Left hand rule
• Describe Fleming’s left hand rule:

  > The forefinger points in the direction if the magnetic field

  > The second finger points in the direction of current flow
• If the direction of current in a current carrying wire placed in a uniform magnetic field is reversed, what happens to the force?

  The direction of the force is reversed
• How does an electric motor work?

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

  > The forces in the two sides perpendicular to the field experience forces in opposite directions

  -> This causes a rotational effect
• Explain how a loudspeaker works:

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

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

  > This produces a force which causes the cone to vibrate
• How is the pitch 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 ends of the conductor
• What can be said about the direction of the magnetic field produced by an induced current?

  > The direction if 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
• What are two ways that the generator effect is used to generate different types of current?

  > In an alternator to produce a.c

  > In a dynamo to produce d.c
• What electromagnetic effect does a microphone take advantage of and how?

  > The generator effect

  > It converts the pressure variations in sound waves into alternating current in a circuit
• Describe the makeup of a basic transformer:


  A primary coil and a secondary coil of wire wrapped around an iron core
• Explain how a transformer works:

  > An alternating current flows through the primary coil

  > This alternating current induces an alternating magnetic field

  > The alternating magnetic field in the iron core induced an alternating potential difference in the secondary coil

  > If the circuit is complete, an alternating current flows in the secondary coil
• How does a dynamo work?

  > The coil rotates and the magnetic field is fixed

  > As the coil rotates, it generates a potential difference in one direction

  > The use of a split ring commutator means that once the coil has passed the upright position, the connections are reversed

  -> As a result, the direction of the current output is always in the same direction
• How do alternators work?

  > A rotating magnetic is used with a fixed coil of wire

  > As the magnet rotates, the direction of the field through which the coil passes alternates