Topic 13-Electromagnetic Induction

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

  Current
• What happens to electrons in a conductor when a magnetic field changes?

  They move to one side of the conductor
• What occurs if the conductor is connected in a circuit?

  A current will flow
• What does the induced current produce?

  Its own magnetic field
• How does the direction of the new magnetic field relate to the original field?

  It opposes the original change
• What is the process of small-scale current induction?

  • Spinning a coil in a magnetic field induces current
  • Passing a wire through a magnetic field shows deflection in an ammeter
• Describe the large-scale production of current in a thermal power station.

  • Water heats to steam via fossil fuels/nuclear fission
  • Steam drives a turbine connected to a coil in a magnetic field
  • Spinning coil generates current
• What factors affect the size of the current or voltage produced?

  Number of coils, speed, magnetic field strength
• What happens to the current in an alternator every half turn?

  It switches direction
• Which rule is used to show the direction of current in an alternator?

  Left Hand Rule
• What does a dynamo do differently than an alternator?

  It uses a commutator to keep current positive
• How do microphones and loudspeakers work in relation to current induction?

  • Microphones: Sound waves cause coil movement, inducing current
  • Loudspeakers: Current flows into coil, causing cone movement and sound
• What is the role of transformers in electrical energy transmission?

  • AC in primary coil creates changing magnetic field
  • Induces current in secondary coil
  • Step-up transformers increase voltage; step-down transformers decrease voltage
• What happens if the primary current in a transformer is DC?

  No current is induced in the secondary coil
• What is the relationship between the number of coils and voltage in a step-up transformer?

  More coils increase voltage
• What is the relationship between the number of coils and voltage in a step-down transformer?

  Fewer coils decrease voltage
• How is electrical energy transferred in the National Grid?

  At high voltages from power stations
• Why is electrical energy transformed to lower voltages for domestic use?

  • Improves transmission efficiency
  • Reduces energy loss due to heating effect
  • High currents cause more energy loss
• What happens to voltage and current when the voltage is decreased near towns?

  Voltage decreases, current increases
• Summarize the functions of step-up and step-down transformers.

  • Step-up transformers: Increase voltage
  • Step-down transformers: Decrease voltage
• What is the power relationship in a transformer with 100% efficiency?

  Power of primary equals power of secondary
• What is the formula for power in a transformer?

  $V_{primary} \times I_{primary} =$$V_{secondary} \times I_{secondary}$