Electrical Circuit
Electricity and Magnetism

Building and describing circuits with parallel connections

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

Describing bulbs in parallel.

Here you will want to concentrate on the following two aspects of adding bulbs in parallel:

  • There is more current in the battery.
  • The energy shifted by each bulb remains constant, so long as there is only one bulb in each loop.

(You might want to assume simple proportionalities, as a first approximation.)

Other changes follow from this, and you may want to use the energy and charge flow descriptions as well, although these should not be central at this point. The whole circuit is important here, so we suggest building one or two simple ones, showing how the labels might be used, and then providing a few challenges to construct with the class as a way of fixing the behaviour of the circuit elements in their minds.

What Happens During this Activity

For selected circuits, we suggest that you use a mixture of current and potential difference labels, and compare the resultant changes to these labels as the number of loops is increased.

Alternatively you might want to set some circuits that bring together some of the challenges through this topic. For example, one could ask the pupils to build a circuit that flattens the battery twice as quickly. You could also ask for a circuit that flattens the battery at half the rate of the first one, so setting a harder challenge.

Again, use the labels to provide a set of reasons for this being a solution.

Much greater complexities are possible, for example: Build a circuit where three lamps are not all equally bright.

To develop this: Now add arrows to show the amounts of energy shifted by the lamps and the energy supplied by the cell.

And, even further: Now add arrows to show how much current passes through each bulb and through the cell.

So there are lots of possibilities for discussion foci here. You will need to choose wisely, with the abilities and interests of your class in mind.

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