ATL
Critical-thinking skills: Practice observing carefully in order to recognise problems.
What determines the amount of electric current flowing through a conductor? We already know that a potential difference across the conductor is required to make the electrons move and carry energy. But what is the effect of the conductor material?
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Inquiry: To investigate the effect of conducting material on the electric current.
Equipment
Voltmeter (Multimeter)
Ammeter (Multimeter)
Connecting wires (with crocodile clips)
Power supply unit or battery pack
Variable resistor (rheostat)
Various pieces of conducting wire
Method
Connect the circuit components as shown in the Figure below.
Connect one of the conducting materials between the connecting clips in the circuit as shown.
Variables
Discuss: What independent variable will you change in this experiment? How will you change it? How will you measure its value?
What dependent variable will you measure?
What must be controlled (kept the same)?
Hypothesis
Suggest a relationship between the independent and the dependent variables you have identified. Justify this hypothesis in terms of what you know about electric current in circuits.
Before you begin, carry out preliminary measurements with a sample of material and decide on the appropriate range and interval for your readings.
Look carefully at the meters with which you have been provided. What is the smallest measurement they can make? This is called the minimum scale division. Record this smallest scale value.
Results
Make suitable measurements of the way the current in the circuit is affected for different materials. Record these measurements in a table.
At the top of the table, record the minimum scale uncertainty. For example, if your voltmeter has a scale that looks like the one below, the smallest scale division is 0.1 V. The minimum scale uncertainty is usually take to be half this value, because you can more or less estimate whether the needle of the meter is above or below half way between the scale divisions.
The minimum scale uncertainty is the limit of accuracy of your meter, such that when you read the meter you could be 'wrong' by this amount. You would then write the minimum scale uncertainty for your voltage values as:
potential difference (Volts) ± 0.05 V
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Analysis
Present the data in a suitable way so that you can find a relationship between the potential difference, V, and the current, I.
Conclusion
Identify a relationship in your data. State the relationship.
Now share your results with the class and compare to the results for other groups.
What was similar about the results? What was different about the results?
Evaluate the hypothesis you made, now that you have results.
Evaluation
Review your results. Comment on the following:
How consistent are they? Do they all fall close to the expected relationship, or are they 'scattered' around it?
Was there an intercept on your graph? Is this to be expected, or is this an error?
How significant (important) was the minimum scale uncertainty to the error in your results? Were there other sources of error?
What could you do to minimize these sources of error?
Assessment opportunities
In this activity you practice skills that are assessed using Criterion C: Processing and evaluating.