transformers

• what are the 3 components of a transformer?

  • primary coil
  • secondary coil
  • both coils are wrapped around an iron core
• what is changed by a transformer?

  the voltage in a wire carrying an alternating current.
• Vp/Vs = Np/Ns
• Which of these does the potential difference across a pair of coils depend on?

  the number of turns on a coil.
• what are transformers used for in terms of electricity?

  used to increase the voltage of electrcity so it can be transmitted long distances through cables. A step-up transformer is used to increase the voltage to 400,000 v to be transmitted long distances.
• why is transmitting electricity at high voltages efficient?

  high voltages reduce the energy that is lost as heat due to the resistance of the cables.
• what is the equation for power, linking voltage and current?

  power = voltage x current
• why are step-up transformers used to increase the voltage that we use to transmit electricity?

  this reduces the current in the secondary coil and reduces the energy lost as heat during transmission.
• why is DC current not used for the national grid?

  transformers are used to minimise wasted energy during transmission. DC does not work with transformers because the secondary coil of a transformer needs to be linked with an alternating magnetic field. Only an AC can achieve this.
• step-up transformers have a higher potential difference across the secondary coil than the primary coil.
• step-down transformers have more potential difference across the primary coil than the secondary coil.
• Why is iron used as the core of a transformer?

  it is easily magnetised
• How the charger of an electric toothbrush works

  1. There is a wire coil in the charger that takes the electricity from the mains supply

  2. There is a second coil in the toothbrush

  3. Alternating pd from the mains supply is applied across the primary coil in the charger

  4. AC is generated in the primary coil

  5. AC creates a continuously changing magnetic field in the iron core that passes through the secondary coil

  6. Alternating pd produces an AC in the secondary coil that charges the battery of the toothbrush
• Despite insulation of a plastic layer on both the charger and the toothbrush for water resistance, the charger works