Energy Transfers

• A householder always fills the electric kettle to the top, even when only enough boiling water for one small cup of coffee is wanted.

  Explain how the householder is wasting money.

  it takes more time to boil

  so, more energy transferred

  which costs more money
• What is meant by direct current?

  current that is always in the same direction
• When the air near the freezer compartment is cooled, the energy of the air particles is decreased
• The spaces between the air particles are decreased. The density of the air is increased

   
•  Reducing the amount of energy used by washing machines could reduce the amount of carbon dioxide emitted into the atmosphere. Explain why.

  fewer power stations needed

  less fuel is burned
• Suggest how data collected and displayed by the electronic device could be useful to the homeowner.

  can look for trends

  help reduce energy use

  reduce bills
• The ceramic bricks are surrounded by 'super-efficient' insulation. Explain why.

  Reduce of energy transfer so bricks are hotter than longer
• Energy is transferred through the metal casing by conduction
• The warm air rising from the heater transfers energy to the room by convection
• Give one advantage of using underground power cables rather than overhead power cables.

  can’t be seen
• It is better for the environment if people switch off their televisions, instead of leaving them in ‘stand by’ mode.Explain why

  It uses electricity generated from fossil fuels producing CO2 which contributes to global warming
• electric current

  flow of charge
• potential difference

  work done per coulomb of charge
• The resistance of the metal filament inside the bulb increases as the potential difference across the bulb increases. Explain why.


  metals contain free electrons so as the temperature of filament increases ions vibrate faster electrons collide more with ions
• The air inside the fridge forms a convection current when the fridge door is closed. Explain why

  air near freezer compartment is cooled

  cool air is dense so air falls and the air at the bottom is displaced