Investigating a real circuit
What the activity is for
Having had the chance to think through their ideas aided by the diagnostic questions, the pupils are now shown a
real circuit and are encouraged to bring their ideas out into the open through class discussion.
The big circuit consists of a power supply (battery) and bulb. The power supply is at the front of the room, the bulb at the back, and the connecting wires run right round the perimeter of the room, taped to the classroom walls.
Why use such a big circuit? The idea here is that the big circuit helps focus attention on the need for some mechanism to shift energy from the battery to the bulb and, most importantly, that the bulb lights very quickly, even when it is some distance from the battery.
What to prepare
- a mounted bulb (A 24 watt, 12 volt bulb works very well, being big enough for the whole class to see.)
- 12 volt power supply
- 2 very long leads
What happens during this activity
First of all draw the pupils' attention to the size of the big circuit. They are actually sitting in the middle of it and:
it's an absolute whopper of a circuit! With due ceremony, build up slowly to switching on the big circuit, asking the pupils to predict whether the bulb will light straightaway.
Teacher: What happens when the switch is closed?… Bulb heats up and lights up.
Teacher: Where does this energy come from in the first place?… The battery.
This happens pretty quickly, even though there is a big distance between battery and bulb:
Teacher: How does the energy get from battery to bulb?
Teacher: Why does it happen so quickly?
Teacher: We can see light being given out from the bulb and we can feel the heating effect, but we cannot see how this happens. What is going on in the big circuit to allow the bulb to light?
We think that in response to what happens with the big circuit, pupils will talk about electricity, electric current, charge flow and energy. These ideas can be built upon by developing a model for simple electric circuits.
Teacher: The aim of the next few lessons is for you to become experts in understanding and explaining how electric circuits work. Although we cannot see what is happening inside the wires and other parts of the circuit, scientists have a model to explain what is going on. We want to understand this electric circuit model.