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Faulty Circuits
AKA: Fault Finding


Simple electrical circuits are made up with hidden faults. Students must use logic to determine the fault and correct it.


This practical not only teaches students about simple electrical circuits but also about fault finding, logic and problem solving.

It involves a series of five identical simple circuits containing a cell, a lamp, a switch and connecting wires. In four of the circuits there is one fault, the fifth is fully working. Students must determine what the fault is in each of the four circuits by testing it with components from the others. The student should end up with four working circuits and one which comprises all four faulty components.

The hidden faults are as follows:

Cell – a dead battery can be used ensuring there is no discharge or residue coming for the cell.

Leads – one end of the lead needs to be insulated from the plug by a piece of insulating tape but still held firmly in place by the plug housing.

Switch – One of the switches needs to be damaged so that it does not operate. If a simple push switch is used, a dab of glue on one of the contacts will mean the contacts will not come together and therefore there will be a break in the circuit.

Lamp – A dead lamp can be used.

The problem with this practical from a technician point of view is that once the components are returned, they have to be checked to determine the faulty and the working. An easy way to do this is to dab a spot of Tippex or paint onto each faulty component which cannot easily be seen by the student. This will ensure when you get the components back, they can easily be sorted without having to test them all individually.

A stock of dead cells and lamps can be amassed over time by routinely testing these components as they come back from practicals.


 CautionEnsure dead cells are not leaking.

The contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.