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Key Questions:

1. (Physics only) How do loudspeakers and headphones use the motor effect?
   • (Physics only) Loudspeakers and headphones use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves.
2. (Physics only) How do moving coil loudspeakers and headphones work?
   • (Physics only) Headphones and moving-coil loudspeakers work by transforming electrical signals into sound. They do this by using an electromagnet held inside a permanent magnet's field. The electric current around the amplifier constantly changes, and in changing it also changes the magnetic field around the electromagnet. This causes changing attraction and repulsion between the two magnets making the electromagnet move backwards and forwards. This movement causes sound waves.
3. (Physics only) How are potential differences induced across the ends of conductors?
   • (Physics only) If an electrical conductor moves relative to a magnetic field or if there is a change in the magnetic field around a conductor, a potential difference is induced across the ends of the conductor.
4. (Physics only) What is the generator effect?
   • (Physics only) The generator effect occurs if a conductor is part of a complete circuit and therefore induces a current.
5. (Physics only) What effect does an induced current have?
   • (Physics only) An induced current generates a magnetic field that opposes the original change, either the movement of the conductor or the change in magnetic field.
6. (Physics only) What factors affect the size of the induced potential difference or induced current?
   • The factors that affect the size of the induced potential difference/induced current are the speed of the magnet or wire, the strength of the magnet, the number of turns or loops in the coil or the area of the coil.
7. (Physics only) What are the principles of the generator effect?
   • the principals of the generator effect are: 1. A moving wire moves between a magnetic field line 2. A potential difference is induced across the ends of the wire 3. An induced current passes along the wire
8. (Physics only) How does the generator effect generate A.C in an alternator? What factors can affect the current in an alternator?
   • An alternator uses the generator effect as its slip rings are connected to the ends of the coil to allow the coil to spin without winding the wire around itself. The brushes are conducting contacts that touch the slip rings and complete the circuit. The size of the induced current can be increase by increasing the number of turns on the coil, using more powerful magnets and turning the coil faster.
9. (Physics only) What would the graph showing potential difference generated in the coil against time look like?
   • The graph showing potential difference generated in the coil against time would show a transverse wave oscillating through the normal line.
10. (Physics only) What do microphones convert into variations in current in electrical
    • (Physics only) Microphones use the generator effect to convert the pressure variations in sound waves into variations in current in electrical circuits.
11. (Physics only) Explain how a moving-coil microphone works?
    • (Physics only) Sound waves make the diaphragm vibrate. The vibrations make the coil move back and forth, causing a varying current to flow as the coil moves over the permanent magnet.
12. (Physics only) How does the generator effect generate D.C in an dynamo?
    • A dynamo is used to generate a direct current by moving the coil in a magnetic field. As the coil turns it cuts the magnetic field lines. This induces a potential difference between the end of the coil. This causes an induced current to pass through the coil and through the circuit the coil is a part of. The split ring commentator rotates with the coil and maintains a complete circuit with the external circuit. Each half turn the sides of the coil connect to the opposite side of the circuit so the direction of the induced potential difference doesn't change.