AQA · A-Level · Physics
Course version: 7408 · Version from Sept 2016
Students should appreciate the use of a variety of sensors to collect…
Full specification wording
Difference between analogue and digital signals (A-level only): Students should appreciate the use of a variety of sensors to collect analogue data.
Sensors convert a physical quantity into an electrical signal, usually a voltage, that varies continuously and is therefore analogue.
Checked against the AQA 7408 specification (opens in a new tab) on .
- Point 4 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Sensors convert a physical quantity into an electrical signal, usually a voltage, that varies continuously and is therefore analogue. A thermistor changes resistance with temperature, an LDR changes resistance with light intensity, a strain gauge changes resistance when stretched, and a microphone produces a voltage from pressure variations. A potential divider containing the sensor converts its resistance change into a voltage that can be sampled and digitised. Sensors allow automatic, continuous and remote monitoring, and their analogue outputs are well suited to pulse code modulation. The choice of sensor depends on the quantity measured, its range, sensitivity, linearity and response time.
What earns the marks
- A sensor converts a non-electrical physical quantity, such as temperature, light intensity, strain or pressure, into an electrical signal.
- The output of many sensors is a continuously varying voltage, so it is an analogue signal suitable for sampling and digitisation.
- A potential divider is often used to convert a resistance change in a thermistor, LDR or strain gauge into a measurable voltage.
- Different sensors suit different quantities and ranges, so selection depends on sensitivity, linearity, response time and operating conditions.
- Sensors enable automatic, continuous or remote data collection, which is more practical than manual reading in many experiments.
- The analogue sensor output can be processed by an analogue-to-digital converter and then transmitted or stored digitally.
Common mistakes and how to put them right
Treating a sensor output as automatically digital.
Put it right by identifying the analogue nature of the output.
Assuming any sensor can measure any quantity.
Put it right by matching the sensor to the quantity and range required.
Ignoring the potential divider.
Put it right: A resistance change alone is not a voltage, so a potential divider or similar circuit is needed to produce a measurable signal.
Exam tips
- Name the physical quantity, the sensor and the electrical output when describing a measurement system.
- Explain how a potential divider converts a resistance change into a voltage change, referring to the fixed resistor and the sensor.
- Link the analogue sensor output to sampling and analogue-to-digital conversion to show why the data can be processed digitally.
Try the lesson
The start of the Difference between analogue and digital signals (A-level only): Students should appreciate the use of a variety of sensors to collect analogue data. lesson, made from checked teaching notes for this specification point.
Have a go first
Which sensor is most suitable for collecting analogue data about the temperature of a water bath in a school laboratory?
Listen
Sensors convert a physical quantity into an electrical signal, usually a voltage, that varies continuously and is therefore analogue. A thermistor changes resistance with temperature, an LDR changes resistance with light intensity, a strain gauge changes resistance when stretched, and a microphone produces a voltage from pressure variations. A potential divider containing the sensor converts its resistance change into a voltage that can be sampled and digitised. Sensors allow automatic, continuous and remote monitoring, and their analogue outputs are well suited to pulse code modulation. The choice of sensor depends on the quantity measured, its range, sensitivity, linearity and response time. A strong answer earns marks for these points. A sensor converts a non-electrical physical quantity, such as temperature, light intensity, strain or pressure, into an electrical signal. The output of many sensors is a continuously varying voltage, so it is an analogue signal suitable for sampling and digitisation. A potential divider is often used to convert a resistance change in a thermistor, LDR or strain gauge into a measurable voltage. Different sensors suit different quantities and ranges, so selection depends on sensitivity, linearity, response time and operating conditions. A common slip: Treating a sensor output as automatically digital: most sensors give a continuously varying analogue voltage. Instead, identifying the analogue nature of the output. Exam tip: Name the physical quantity, the sensor and the electrical output when describing a measurement system.
Key words
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Analogue data collection
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Sensor transduction
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Potential divider circuits
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Automatic and remote monitoring
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See every definition
- Analogue data collection
- Sensors convert a physical quantity into an electrical signal, usually a voltage, that varies continuously and is therefore analogue.
- Sensor transduction
- A sensor converts a non-electrical physical quantity, such as temperature, light intensity, strain or pressure, into an electrical signal.
- Potential divider circuits
- A potential divider containing the sensor converts its resistance change into a voltage that can be sampled and digitised.
- Automatic and remote monitoring
- Sensors allow automatic, continuous and remote monitoring, which is more practical than manual reading in many experiments.
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