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Current - Voltage (IV) characteristics of components
Construct circuits to investigate I–V characteristics of a resistor, filament lamp and diode
Check your understanding with these quick common questions. Use the drop down boxes to see the correct answers.
IV characteristics
IV characteristics of a component sounds confusing, it doesn't need to be. This investigation simply measures the current and potential difference (voltage) in a circuit with one of three components. A resistor, a filament bulb and a diode. Current, Voltage and resistance are all linked. Some components are quite special and follow a law, called Ohm's law. If they show this pattern they are called an Ohmic conductor. Resistors will show this pattern. Light bulbs get hot and the resistance goes up, so they do not follow this pattern. Diode's only allow current to flow one way, so they have an usual pattern too. You will need to recognise these graphs.
What are the control, Dependent & Independent variables?
What are the control, Dependent & Independent variables?
This is more of a procedure than an investigation, so you are less likely to be asked about these variables.
Independent variable: Potential difference (voltage) across the component.
Dependent variable: Current through the component.
Control variables: Temperature of components; same meters/wires; voltage step size/time at each step.
What special pieces of equipment are required?
What special pieces of equipment are required?
Ammeter
Voltmeter
Variable resistor
How can accuracy and Validity be improved?
How can accuracy and Validity be improved?
Accuracy can be improved by using a narrower crocodile clip so you can measure the length of the wire exactly. Digital ammeters and voltmeters have a higher resolution than analogue ones.
Validity can be improved by: A variable resistor can be used to adjust the potential difference. The components can quickly overheat if left on and this increases resistance. The circuit should be switched off quickly after taking measurements.
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What do typical results look like? (label the graphs)
What do typical results look like? (label the graphs)
Describe: Resistor gives a straight line (Ohm’s law). A
Lamp curves (resistance rises when hot). B
Diode conducts in one direction only above a threshold. C
Explain: Heating raises resistance in the filament; Diodes only allow current to flow in one direction.
Outline a basic method
Outline a basic method
Set up a circuit with power supply
Add an ammeter in series
Add a voltmeter in parallel.
Measure Potential difference (Voltage) and Current for each component
Use the variable resistor to adjust the potential difference
Reverse the current and repeat (to give the data for the left side of the graph)
You could Use V= IR and rearrange to Resistance = Voltage / Current to calculate resistance.
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