P1aL5 Energy Diagrams

Key Words

Conservation of Energy - Energy can not be created nor destroyed; it's turned from one form to another.

Electrical energy - energy transferred in the form of electricity

Energy input - the total amount of energy put in

Energy output - the useful energy got out

Energy Transfer Diagram - a diagram that shows us in a picture what happens to the energy in block arrow form.

Sankey Diagram - a diagram that shows the energy transfers and changes in block arrow form, with wasted energy pointing down.

Heat energy - energy flowing from a hot object to a cold object.

Transformation - turning one type of energy into another.

Wasted energy - energy lost in non-useful forms like noise and heat

Test Yourself

Homework
Physics GCSE
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Grade E

The energy transfer diagram shows how an ordinary light bulb transfers most of its energy into heat, and very little into light.

 

All devices that transform energy waste some of it (or a lot of it in the case of a light bulb).  The bulb above has an energy input of 100 J.  Of that 98 J is lost as heat, and 2 J is turned to light.  The waste of energy does NOT mean that the energy has been destroyed; it's been wasted.

100 J (input) = 98 J (heat) + 2 J (light)

A Sankey diagram shows the waste energy as a downward pointing arrow.

This Sankey diagram shows that in a car engine, for every 1000 J energy from the petrol, 700 J are wasted.  Only 300 J are useful.

 

Grade C

We can use Sankey diagrams where there are several sources of lost energy.  We can also draw them to scale as shown below:

 

We can see that of 1000 J:

  • 150 J is lost up the exhaust;

  • 550 J is used to make the engine turn;

  • 300 J is used to make the car go along the road.

If you add up all the parts, the output energy all adds up to 1000 J.  The output energy must add up to the input energy.

 

Grade A

Here is a more complex energy transformation diagram, the sort used by engineers.  This one is for an aeroplane engine.

The letters "hp" stand for horsepower.  1 hp = 746 Watts.  Nowadays we use PS (Pferdstarke) for horsepower, where 1 PS = 750 W.

 

Electric vehicles waste less energy.  And they have been around as long as petrol cars.  However they have a limited range, about 100 - 200 km, have heavy batteries, and take a long time to charge up.