AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Students should be able to use graphs to explore whether circuit elements…
Full specification wording
Resistors: Students should be able to use graphs to explore whether circuit elements are linear or non-linear and relate the curves produced to their function and properties.
A characteristic graph tells you what a component does.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 12 of 13
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A characteristic graph tells you what a component does. Plot current against potential difference and read the shape. A straight line through the origin means a linear, ohmic element whose resistance is constant, such as a fixed resistor at constant temperature. A curve that bends over with a falling gradient means resistance rising with current, which is a filament lamp heating up. A line that stays at zero one side and rises steeply the other means a diode, which conducts one way only. Anything not a straight line through the origin is non-linear, and for those you calculate R = V ÷ I separately at each point. The shape is never decoration; it is the evidence you quote when explaining what the component is for.
What earns the marks
- Identifying the graph as linear or non-linear from its shape.
- Naming the component consistent with that shape.
- Calculating resistance at a stated point using R = V ÷ I.
- Relating the shape to a property or use of the component, such as a lamp heating up.
Common mistakes and how to put them right
Calling any line through the origin linear even when it is clearly curved.
Describing a diode characteristic as a straight line because part of it is.
Using a single resistance value across a curved characteristic.
Describing the shape without saying what it means about the component.
Exam tips
- Answer shape questions in two halves: what the graph shows, then what that means physically.
- Where a graph is curved, say resistance is not constant and then support it with two calculated values.
- Check the axes before commenting, since some papers plot potential difference on the vertical axis.
Try the lesson
The start of the Resistors: Students should be able to use graphs to explore whether circuit elements are linear or non-linear and relate the curves produced to their function and properties. lesson, made from checked teaching notes for this specification point.
Have a go first
A graph of current against potential difference for a fixed resistor at constant temperature is plotted. What shape is the graph?
Listen
A characteristic graph tells you what a component does. Plot current against potential difference and read the shape. A straight line through the origin means a linear, ohmic element whose resistance is constant, such as a fixed resistor at constant temperature. A curve that bends over with a falling gradient means resistance rising with current, which is a filament lamp heating up. A line that stays at zero one side and rises steeply the other means a diode, which conducts one way only. Anything not a straight line through the origin is non-linear, and for those you calculate R = V ÷ I separately at each point. The shape is never decoration; it is the evidence you quote when explaining what the component is for. A strong answer earns marks for these points. identifying the graph as linear or non-linear from its shape. naming the component consistent with that shape. calculating resistance at a stated point using R = V ÷ I. relating the shape to a property or use of the component, such as a lamp heating up. Exam tip: Answer shape questions in two halves: what the graph shows, then what that means physically.
Key words
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linear
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non-linear
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characteristic graph
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diode
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See every definition
- linear
- A straight line through the origin on a current against potential difference graph, meaning an ohmic element whose resistance is constant.
- non-linear
- Anything on a current against potential difference graph that is not a straight line through the origin.
- characteristic graph
- A graph plotting current against potential difference that tells you what a component does.
- diode
- A component whose characteristic stays at zero one side and rises steeply the other, so it conducts one way only.
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