Plan an experiment to investigate how the thickness of a metal wire affects its resistance. Resistance = potential difference across the wire / current in the wire.
You have six lengths of metal wire, each of different thickness, an ammeter, voltmeter, power supply, connecting leads and micrometer. You may use other apparatus normally available in a school laboratory. You are not required to do the experiment.
Draw a circuit diagram; explain briefly how to carry out the investigation; state the key variables to keep constant; draw a results table with column headings and units (no readings required); explain how to use the readings to reach a conclusion.
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One correct answer. This part can’t be checked automatically yet, so compare your own working with it.
Circuit diagram (one mark): connect the power supply, the ammeter and the test wire in series, and label the wire. Connect the voltmeter in parallel across that wire only, so the ammeter measures the current in the wire and the voltmeter the potential difference across it.
Method (two marks): measure the thickness (diameter) of each of the six wires with the micrometer. Then connect each wire in turn, take the current and potential difference readings, and calculate its resistance from resistance = p.d. ÷ current.
Variables to keep constant (one mark): all six pieces should be the same length and made of the same metal. Results table (one mark): give columns for thickness (diameter) and resistance, each headed with its unit, for example thickness / mm and resistance / Ω; you can add columns for p.d. / V and current / A.
Conclusion (one mark): compare the resistance values to see whether resistance changes as the thickness changes, or plot a graph with thickness (diameter) on one axis and resistance on the other and describe the trend it shows.
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