OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(ii) techniques and procedures used to investigate potential divider…
Full specification wording
Potential dividers: (ii) techniques and procedures used to investigate potential divider circuits which may include a sensor such as a thermistor or an LDR.
To investigate a potential divider, build a series circuit with a fixed resistor and a sensor, such as a thermistor or a light-dependent resistor (LDR), connected across a d.c. supply.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 4 of 4
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
To investigate a potential divider, build a series circuit with a fixed resistor and a sensor, such as a thermistor or a light-dependent resistor (LDR), connected across a d.c. supply. Measure the supply voltage and the output voltage across one component with a voltmeter connected in parallel. Vary the physical condition: warm or cool the thermistor, or change the light intensity on the LDR, and record how the sensor resistance and the output voltage change. For a thermistor with negative temperature coefficient, resistance falls as temperature rises, so the voltage across it falls while the voltage across the fixed resistor rises. Plot a graph of output voltage against temperature or light intensity and compare with the predicted divider equation.
What earns the marks
- Set up a series divider with a fixed resistor and a sensor such as a thermistor or an LDR across a d.c. supply.
- Connect a voltmeter in parallel with the component whose output voltage is being measured.
- Vary the physical condition, for example temperature for a thermistor or light intensity for an LDR, and record the output voltage.
- Relate the measured output voltage to the changing resistance of the sensor using the divider equation.
- Plot a suitable graph, such as output voltage against temperature or light intensity, and describe the trend.
Common mistakes and how to put them right
Connecting the voltmeter in series with the divider.
Put it right: A voltmeter is connected in parallel with the component across which the potential difference is measured.
Assuming the sensor resistance is constant while the temperature or light intensity changes.
Put it right: The sensor resistance changes, and that change is what alters the output voltage.
Recording only the output voltage without noting the physical condition.
Put it right: Record temperature or light intensity alongside each voltage so the relationship can be analysed.
Exam tips
- State clearly which component the output voltage is measured across, because the direction of the voltage change depends on this choice.
- Describe the control of variables, such as keeping the supply voltage constant while changing temperature or light intensity.
- Use a graph or table to show the trend and link it back to the divider equation rather than listing readings alone.
Try the lesson
The start of the Potential dividers: (ii) techniques and procedures used to investigate potential divider circuits which may include a sensor such as a thermistor or an LDR. lesson, made from checked teaching notes for this specification point.
Listen
To investigate a potential divider, build a series circuit with a fixed resistor and a sensor, such as a thermistor or a light-dependent resistor (LDR), connected across a d.c. supply. Measure the supply voltage and the output voltage across one component with a voltmeter connected in parallel. Vary the physical condition: warm or cool the thermistor, or change the light intensity on the LDR, and record how the sensor resistance and the output voltage change. For a thermistor with negative temperature coefficient, resistance falls as temperature rises, so the voltage across it falls while the voltage across the fixed resistor rises. Plot a graph of output voltage against temperature or light intensity and compare with the predicted divider equation. A strong answer earns marks for these points. Set up a series divider with a fixed resistor and a sensor such as a thermistor or an LDR across a d.c. supply. Connect a voltmeter in parallel with the component whose output voltage is being measured. Vary the physical condition, for example temperature for a thermistor or light intensity for an LDR, and record the output voltage. Relate the measured output voltage to the changing resistance of the sensor using the divider equation. A common slip: Connecting the voltmeter in series with the divider. Instead, a voltmeter is connected in parallel with the component across which the potential difference is measured. Exam tip: State clearly which component the output voltage is measured across, because the direction of the voltage change depends on this choice.
Key words
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Sensor resistance and physical conditions
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Output voltage as a function of sensor resistance
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Graphing and interpreting experimental data
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See every definition
- Sensor resistance and physical conditions
- Warm or cool the thermistor, or change the light intensity on the LDR, and record how the sensor resistance and the output voltage change.
- Output voltage as a function of sensor resistance
- Relate the measured output voltage to the changing resistance of the sensor using the divider equation.
- Graphing and interpreting experimental data
- Plot a graph of output voltage against temperature or light intensity and compare with the predicted divider equation.
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