Investigating the resistance of a wire
Investigating the Resistance Of A Wire
A simple investigation of the factors affecting the resistance of a wire.
For each student group
Cells, 1.5 V, with holders, 2
Crocodile clips, 2
Ammeter (0 - 1 amp), DC
Leads, 4 mm, 5
Wire available for class use (see technical notes)
Power supply, 0 to 12 V, DC (OPTIONAL)
Metre rule (OPTIONAL)
Insulating tape (OPTIONAL)
Digital and analogue ammeters, 0-1 A (OPTIONAL)
Digital and analogue voltmeters, 0-12 V (OPTIONAL)
Micrometer (OPTIONAL)
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.
When using a power supply, high currents will cause the safety cut-out on the power packs to automatically switch it off. If short lengths of wire are used with relatively high currents and voltages, then significant electrical heating may also occur. Students should be encouraged to adjust the voltage to keep currents small with every set of readings. At each stage they can connect the circuit, take readings quickly and then disconnect the power supply.
If you use a mains power supply, use one that is designed to limit the output current to about 1 amp, and preferably with a current overload indicator.
Read our standard health & safety guidance
The following apparatus should be available for class use:
Selection of reels of Eureka wire (also known as Constantan or Contra) of different gauges, e.g. 0.71 mm (22 SWG), 0.46 mm (26 SWG), 0.32 mm (30 SWG) and 0.24 mm (34 SWG).
Selection of reels of different wires (e.g. copper, Eureka, iron) of same gauge (e.g. 34 SWG).
a Connect up a series circuit of two cells,
A simple investigation of the factors affecting the resistance of a wire.
For each student group
Cells, 1.5 V, with holders, 2
Crocodile clips, 2
Ammeter (0 - 1 amp), DC
Leads, 4 mm, 5
Wire available for class use (see technical notes)
Power supply, 0 to 12 V, DC (OPTIONAL)
Metre rule (OPTIONAL)
Insulating tape (OPTIONAL)
Digital and analogue ammeters, 0-1 A (OPTIONAL)
Digital and analogue voltmeters, 0-12 V (OPTIONAL)
Micrometer (OPTIONAL)
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.
When using a power supply, high currents will cause the safety cut-out on the power packs to automatically switch it off. If short lengths of wire are used with relatively high currents and voltages, then significant electrical heating may also occur. Students should be encouraged to adjust the voltage to keep currents small with every set of readings. At each stage they can connect the circuit, take readings quickly and then disconnect the power supply.
If you use a mains power supply, use one that is designed to limit the output current to about 1 amp, and preferably with a current overload indicator.
Read our standard health & safety guidance
The following apparatus should be available for class use:
Selection of reels of Eureka wire (also known as Constantan or Contra) of different gauges, e.g. 0.71 mm (22 SWG), 0.46 mm (26 SWG), 0.32 mm (30 SWG) and 0.24 mm (34 SWG).
Selection of reels of different wires (e.g. copper, Eureka, iron) of same gauge (e.g. 34 SWG).
a Connect up a series circuit of two cells,