Energy Transferred by Working
Electricity and Magnetism

Compensated pathways

Classroom Activity for 14-16 Supporting Physics Teaching

What the Activity is for

Show: current and potential difference both contribute to power.

Here you can show that there are such things as compensated circuits: that is, two circuits where the character of the pathways is different but the power in each pathway is identical.

What to Prepare

  • a MES 2.4 V 50 mA bulb
  • a MES 12 V 100 mA bulb
  • 2 matched ammeters
  • 2 matched voltmeters
  • a 24 V battery
  • a 12 V battery
  • a supply of wires to wire up the two loops, coding by colour

What Happens During this Activity

Set up the two circuits and note the similar brightness of the bulbs. Other combinations of bulbs can be substituted, so long as the powers dissipated by each lamp are identical and the currents and potential differences vary.

Then develop a conversation with your class to bring out the following points.

Bulbs are devices that switch power from an electrical pathway to the lighting and heating pathways. It seems that the power in these pathways is identical. However, the character of the pathways is different: one is of large potential difference and small current, and the other is of a smaller potential difference and larger current. The smaller current in one is compensated for by the larger potential difference.

This very simple idea becomes important when dealing with power distribution, and it's best to introduce it here, without the complexity of transformers.

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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