Electricity & Energy - Objectives

Learning Objectives

  1. Be able to compare the efficiency and cost effectiveness of methods used to reduce energy consumption.
  2. Be able to describe the intended energy transfers/transformations and the main energy wastages that occur with a range of devices.
  3. Interpret and draw a Sankey diagram
  4. Be able to calculate the efficiency of a device using:

efficiency = useful energy transferred by the device

total energy supplied to the device

  1. Be able to calculate the efficiency of a device using:

efficiency = useful power out

total power in

  1. Know that energy can be transferred usefully, stored or dissipated but cannot be created or destroyed.
  2. Know that when energy is transferred and/or transformed only part of it may be usefully transferred/transformed, the rest is wasted.
  3. Know that the greater the percentage of the energy that is usefully transformed in a device, the more efficient the device is.
  4. Give examples of energy transformations that everyday electrical devices are designed to bring about.
  5. Give examples of everyday electrical devices designed to bring about particular energy transformations.
  6. Know that energy is normally measured in joules (J).
  7. Be able to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application.
  8. Be able to consider the implications of instances when electricity is not available.
  9. Know that the rate at which energy is transformed in a device is called power and is calculated

Power (Watts) = Energy transferred (Joules)

Time Taken (Seconds)

  1. Know that the amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which the device transforms energy.
  2. Be able to calculate the amount of energy transferred from the mains using, energy transferred = power x time

(kilowatt-hour, kWh) (kilowatt, kW) (hour, h)

  1. Be able to calculate the cost of energy transferred from the mains using, total cost = number of kilowatt-hours x cost per kilowatt-hour
  2. Know that the power of an appliance is measured in watts (W) or kilowatts (kW).
  3. Know that Power, potential difference and current are related by the equation:

power = current × potential difference

(watt, W) (ampere, A) (volt, V)

  1. Be able to evaluate different methods of generating electricity.
  2. Be able to evaluate ways of matching supply with demand.
  3. Be able to compare the advantages and disadvantages of overhead power lines and underground cables.
  4. Know that in some power stations an energy source is used to heat water. The steam produced drives a turbine that is coupled to an electrical generator.
  5. Know that energy sources include: fossil fuels (coal, oil, gas) which are burned to heat water or air, uranium and plutonium, when energy from nuclear fission is used to heat water, and biofuels which are burned to heat water.
  6. Know that water and wind can be used to drive turbines directly.
  7. Know that electricity can be produced directly from the Sun’s radiation.
  8. Know that in some volcanic areas, hot water and steam rise to the surface. The steam can be tapped and used to drive turbines. This is known as geothermal energy.
  9. Know that small-scale production of electricity may be useful in some areas and for some uses, e.g. hydroelectricity in remote areas and solar cells for roadside signs.
  10. Know that using different energy resources has different effects on the environment. These effects include:
  11. The release of substances into the atmosphere
  12. The production of waste materials
  13. Noise and visual pollution
  14. The destruction of natural habitats
  15. Know that electricity is transferred from power station to consumers along the National Grid.
  16. Understand the uses of step-up and step-down transformers in the National Grid.
  17. Know that, in a step-up transformer, the potential difference across the secondary coil is greater than the potential difference across the primary coil.
  18. Know that, in a step-down transformer, the potential difference across the secondary coil is less than the potential difference across the primary coil.
  19. Know that when an electrical charge flows through a resistor, electrical energy is transformed into heat energy.
  20. Know that increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables.
  21. Know that if a transformer is 100% efficient, then the electrical energy entering the primary side each second is the same as the electrical energy leaving the secondary coil each second
  22. Be able to apply and understand the equation,

Powerprimary = Powersecondary

Vp x Ip = Vs x Is