IGCSE Physics Practical Skills 3: Circuits and Electrical Measurements
Cambridge IGCSE Physics notes on building circuits, connecting ammeters and voltmeters, varying current safely, recording V-I data, and evaluating electrical measurements for 06...
Electrical practical work depends on two questions: where does current flow, and between which two points is potential difference measured? Answer those before connecting a meter.
These independently written notes support the practical skills in Cambridge IGCSE Physics 0625 and 0972.
Ammeter in series
An ammeter measures the current through a component. Place it in series so the same current passes through the meter and component.
Opening a circuit and inserting an ammeter into the current path is different from placing the meter across a component. Connecting an ammeter directly across a supply can produce a very large current and may damage equipment.
Voltmeter in parallel
A voltmeter measures the potential difference between two points. Connect it in parallel across the component being investigated.
Trace the two voltmeter leads. They should end on opposite sides of the target component, not at two points on the same piece of connecting wire.
Build with the supply off
Use this order:
- switch off or disconnect the power supply
- identify the complete series path
- add the ammeter in that path
- add the voltmeter across the target component
- set a variable resistor to limit current initially
- check meter polarity and range
- ask for a circuit check if required
- switch on only to take readings
Disconnect between readings when heating of a component could change its resistance.
Select a meter range
Begin with a range that will not be exceeded. If the reading is safely within the scale, select a more sensitive range when this provides better resolution.
On an analogue meter, read the correct printed scale for the selected range. On a digital meter, include the displayed unit and notice whether the prefix is milli, micro, or the base unit.
Vary the electrical condition
A variable resistor can change current without rebuilding the circuit. Adjust it over a useful range while keeping other circuit features fixed.
For each setting:
- allow the meter display to settle
- read current and potential difference as a pair
- record both immediately
- avoid exceeding component ratings
- switch off between readings if temperature must be controlled
Changing the supply and the variable resistor at the same time makes it harder to state what caused the change.
