P2: Energy resources and energy transfer:

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There are 9 types of energies:

Electrical, kinetic, light, heat, sound, nucleargravitationalchemical and elastic.

Why are the last 4 highlighted? Because these 4 types of energies can be stored.

4.2: Describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational):

Some examples:

  • battery connected to a light bulb: chemical-kinetic-light & heat
  • candle and a box of matches: kinetic-light & heat
  • elastic band and a 'paper pellet': elastic-kinetic
  • bowl of breakfast cereal eaten: solar-chemical-kinetic + heat
  • plant in a pot by the window: light (solar) - chemical

Piece of equipment Input energy Output energy Useful Waste Mains light bulb Electrical Light Thermal Electric fire Electrical Thermal Light Battery Chemical Electrical Thermal

4.3: Understand that energy is conserved:


Law of conservation of energy: Energy cannot be created or destroyed; it can only be transferred from one form to another.

4.4: Recall and use the relationship:

Useful energy input ÷ total energy output

4.5: Describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams:

Example: Drill. Kinetic energy is used in drilling walls but heat and sound is produced as well. Kinetic energy is useful whilst heat and sound is wasted as it is not needed in the drilling process. A measure of how the device converts the energy going in into useful energy is called efficiency.

Efficiency= Amount of useful energy/ total amount of energy supplied to the device.

Example: 1000 joules supplied to the device and 500 joules transformed into useful energy; efficiency= 0.5= 50% efficiency.

The greater the efficiency, the less energy is wasted. 

Sankey diagram for watching a movie on a laptop:

Battery charged to use the laptop: Electrical energy.

Energy that is used: Light and sound energy.

Energy that is wasted: Thermal energy (heat energy).


Input electrical energy: 130 joules

Thermal energy: 90 joules (wasted) 

Light energy: 10 joules (used)

Sound energy: 30 joules (used)

Of 130 joules, 90 joules was wasted and 40 joules was used. Not very efficient.

4.6: Recall that energy transfer may take place by conduction, convection and radiation:

Conduction: is the process of thermal energy transfer without any flow of the material medium. It is from particle to particle (as they move faster, they push on neighbouring particles so they speed up too, occurs mainly in solids.)

In conduction


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