ABSTRACT
We begin by investigating what happens when we use different voltages to make a current flow through a conductor. We use a poor conductor, such as carbon, so that the current will not be too large to measure with an ordinary multimeter. Things to do
A suitable piece of carbon for this investigation is a short length (about 3 cm) of Artists’ charcoal.
Connect a 6 V battery, a multimeter and the piece of carbon in a circuit, as shown in the photograph. Use short leads with crocodile clips at each end.
Leave the positive (red) probe of the meter free. By touching this against different metal contacts in the battery box, you can obtain voltages of 1.5 V, 3 V, 4.5 V and 6 V. Alternatively, use a PSU with switchable output instead of the battery.
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Set the multimeter to its largest current range (500 mA or 1 A). If the readings are too small to read accurately, you can switch to a lower current range.
Take the first reading with the red probe at the 6 V point. Measure the current, using the meter. Record these results in a table: https://www.niso.org/standards/z39-96/ns/oasis-exchange/table">
Voltage (volts)
Current (amps)
Voltage/Current
6
4.5
3
1.5
Repeat with the voltage set to 4.5 V, 3 V and 1.5 V.
What do you notice about the current as we reduce the voltage? To investigate this further, divide each voltage by the corresponding current and write the results in the third column. What do you notice about the values in the third column?
