Energy Transferred by Working
Energy and Thermal Physics

Choosing household lighting

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

To establish that individual choices can make a difference.

What to Prepare

  • two mains lamps of equal brightness, one energy saver (compact fluorescent) and one filament, say 100 watt, complete with their packaging
  • this interactive

What Happens During this Activity

Compare the brightness of the two lamps. They should provide equal illumination, but the conventional filament lamp will cost more energy per second to run (about four times as much typically). Now compare how warm they feel by holding the hand a short distance away.

Show the interactive.

Making savings

Work out with the class how many such lamps they have in their homes. What savings could be achieved if they all swapped? Now work it out for the whole school. This will be a very good practice of estimating – always work to one significant figure only! How many people have to change so that we can shut down one 100 MW power station? Perhaps we could avoid all the arguments about wind turbines in remote areas of natural beauty if we all demanded a bit less energy.

Lamps are easy to compare as most homes are lit using electrical power. Whilst it would be very useful to compare lighting with heating, it'll only be a minority of homes that are all-electric, and so such comparisons are harder to do without much more conversion work. However, if your class can cope with the numbers and arithmetic, this is well worthwhile, if only to convince them that turning a light off to save energy is not the most effective of actions.


Download the interactive for this activity.

Energy Transferred by Working
appears in the relation dU=dQ+dW
is used in analyses relating to Working Engines Thermionic Emission
is a special case of Work
has the special case Potential Energy Kinetic Energy
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