Experiments with switches
Many interesting circuits can be set up with switches in series and in parallel with components.
Apparatus and materials
For each student group
Cells, 1.5 V, with holders, 3
Lamps with holders, 3
Leads, 4 mm, 7
Health & Safety and Technical notes
Various kinds of switches can be used such as a swivelling link, SPST (single pole-single throw) toggle switches, bell pushes etc.
Modern dry cell construction uses a steel can connected to the positive (raised) contact. The negative connection is the centre of the base with an annular ring of insulator between it and the can. Some cell holders have clips which can bridge the insulator causing a 'short circuit'. This discharges the cell rapidly and can make it explode. The risk is reduced by using 'low power', zinc chloride cells not 'high power', alkaline manganese ones.
a Set up the circuit shown. What happens when you open and close the switch?
b Investigate the effect of moving the switch to different points in the circuit.
c Investigate some more complex circuits including two switches.
d Summarize your findings.
1 Many interesting circuits can be set up with switches in series and in parallel with components. Students should be encouraged to think of a switch as ‘breaking’ a circuit. Can they identify the relevant circuit?
2 Simple logic circuits can also be set up. With two switches in series, both switch 1 AND switch 2 have to be closed to produce the desired effect. Connect switches in parallel to each other, and then connect this ‘unit’ into a series circuit. This will show the desired effect if one OR the other switch is closed.
3 It is also valuable to include an ammeter in the circuit. This may show something interesting when there are branches of several lamps or sets of lamps in a circuit, with a switch in each branch.
This experiment was safety-tested in June 2006