Topic 13 Electromagnetic Induction

• What is induced when a wire is moved in a magnetic field?

  Current is induced.
• What happens to electrons in a conductor when it is moved in a magnetic field?

  Electrons move to one side of the conductor as the field changes.
• What occurs if the conductor is connected in a circuit?

  A current will flow through the circuit.
• What does the current produced in a circuit generate?

  It produces its own magnetic field.
• How does the direction of the new magnetic field relate to the original magnetic field?

  The direction of the new field is opposite to the first field.
• What is the process of small-scale current production using a coil of wire?

  • Spinning a coil of wire between two permanent magnets induces a current.
  • A sensitive ammeter can show the current generated (only milliamps).
  • Passing a wire through a magnetic field also shows a deflection in an ammeter.
• Describe the large-scale production of current in a thermal power station.

  • Water is heated to form steam (via fossil fuels or nuclear fission).
  • Steam is put under pressure and forced into a turbine.
  • The turbine rotates, connected to a coil of wire in a strong magnetic field (the generator).
  • Current is generated by the spinning motion of the coil through the magnetic field.
• What factors affect the size of the current or voltage produced in an induction process?

  The number of coils of wire, speed of rotation, and magnetic field strength affect the current/voltage produced.
• How does an alternator produce AC current?

  • Every half turn, the current switches direction.
  • The wire's orientation changes compared to its starting position.
  • The Left Hand Rule can be used to show the direction of the induced current.
• What is the function of a commutator in a dynamo?

  • A commutator reverses the sign of the current flowing from the coil.
  • It ensures the current output remains positive.
  • Every half-turn, the commutator switches the sign of the current.

  
• What type of current does a dynamo produce?

  A dynamo produces DC (direct current).

  
• How do microphones and loudspeakers work in relation to current and sound signals?

  • They produce a current proportional to the sound signal.
  • A fixed magnet is at the center, with a coil of wire around it.
  • Pressure variations in sound waves cause the coil to move, inducing current.
  • The loudspeaker setup is identical, where current causes the cone to move, producing sound.
• What is the role of transformers in electrical energy transmission?

  • AC in the first coil creates a changing magnetic field.
  • This changing magnetic field induces a current in the secondary coil.
  • If the primary current is DC, no current is induced in the secondary coil.
• What happens when there are more coils on the secondary side of a transformer?

  It becomes a step-up transformer, increasing the voltage.
• What happens when there are fewer coils on the secondary side of a transformer?

  It becomes a step-down transformer, decreasing the voltage.
• How is electrical energy transferred in the National Grid?

  Electrical energy is transferred at high voltages from power stations.
• Why is electrical energy transformed to lower voltages for domestic use?

  • To improve the efficiency of transmission.
  • Larger currents cause greater heating effects in wires, leading to energy loss.
  • Increasing voltage reduces current, minimizing energy loss.
• What is the relationship between power, current, and voltage in the context of energy loss?

  As power is constant, increasing voltage reduces current to minimize energy loss.
• What is the formula for power in relation to current and voltage?

  Power is given by \( P = IV \).
• What is the summary of transformer functions?

  • Step-up transformers increase voltage.
  • Step-down transformers decrease voltage.
  • Power for a transformer with 100% efficiency: \( V_{\text{primary}} \times I_{\text{primary}} = V_{\text{secondary}} \times I_{\text{secondary}} \).