induced potential and transformers

• What is induced across the ends of a conductor?

  A potential difference
• When is a potential difference induced in a conductor?

  If the conductor moves relative to a magnetic field
• What happens in a complete circuit when a potential difference is induced?

  There will be an induced current
• What are the two ways to demonstrate the generator effect?

  1. Move a wire in a magnetic field
  2. Move a magnet in and out of a coil
• What happens to the direction of induced potential difference if the movement of the wire is reversed?

  It reverses
• What effect does reversing the polarity of the magnet have on induced current?

  It reverses the induced current
• What type of current is produced if the reversal happens repeatedly?

  Alternating current
• What factors increase the induced potential difference or current?

  Speed of movement, magnetic field strength, turns in coil
• What does an induced current generate around the conductor?

  A magnetic field that opposes the original change
• What is a transformer?

  • A device that changes alternating potential difference
  • Consists of two coils wound around an iron core
• How does an alternating current affect the primary coil of a transformer?

  It produces an alternating magnetic field
• What does the alternating magnetic field in the iron core induce?

  An alternating potential difference in the secondary coil
• What is the relationship between potential differences and number of turns in a transformer?

  V₁/N₁ = V₂/N₂
• Why is iron used for the core of a transformer?

  It is easily magnetised and demagnetised
• How does a transformer work?

  • Alternating current in primary coil creates alternating magnetic field
  • This induces alternating p.d. in secondary coil
• What type of transformer has more turns on the secondary coil?

  Step-up transformer
• What is the efficiency of a transformer if power output equals power input?

  100%
• What are the key terms related to induced potential and transformers?

  • Alternator
  • Dynamo
  • Generator effect
  • Induced
  • Polarity
  • Split-ring commutator
  • Transformer
• What is another name for the generator effect?

  Electromagnetic induction
• How can the direction of an induced p.d. or current be reversed?

  By reversing the movement of the conductor or magnet
• What affects the size of an induced p.d. or current?

  Speed of movement, strength of magnetic field, number of turns
• How does an alternator utilize the generator effect?

  By turning a coil in a magnetic field
• What type of current does a dynamo produce?

  Direct current
• How does a dynamo maintain current flow in the same direction?

  Using a split-ring commutator
• When is the induced p.d. in a dynamo at its maximum?

  When the coil is parallel to magnetic field lines
• How does a microphone utilize the generator effect?

  It converts sound wave pressure variations into electrical current
• What does a transformer do?

  Changes the magnitude of alternating p.d.
• What does a basic transformer consist of?

  Two coils of wire wound around an iron core
• Why is iron used for the core of a transformer?

  Because it is easily magnetised and demagnetised
• How does the ratio of p.d. across the primary and secondary coils relate to the number of turns?

  It is the same as the ratio of turns
• Which type of transformer has fewer turns on the secondary coil?

  Step-down transformer
• What must be true for power to remain the same in a transformer?

  Power output equals power input
• What is the formula for power in terms of voltage and current?

  P = V × I
• What is the induced p.d. in a dynamo during a cycle?

  Varies from zero to maximum twice each cycle
• When is the induced p.d. zero in a dynamo?

  When the coil is perpendicular to magnetic field lines
• What happens to the induced p.d. when the coil lies parallel to the magnetic field lines?

  It is at its maximum
• What is the relationship between the induced p.d. and the frequency of sound waves in a microphone?

  They have the same frequency
• What does the split-ring commutator do in a dynamo?

  Swaps contacts with the circuit every half turn
• What is the role of brushes in a dynamo?

  They allow current to flow out of the coil
• How does the induced p.d. in a dynamo behave during a full cycle?

  It varies from zero to maximum