Components
Physics: Cambridge International A Level, topic 12.1.9
Input Transducers
An input transducer is a circuit that turns a variable outside of the circuit, such as temperature or light, into an electrical signal. Themistors and light dependent resistors (LDR)s can be used to make input transducers.
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Thermistors
- A thermistor is a component whose resistance changes with its temperature.
- Usually increasing temperature decreases the resistance.
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LDRs
- A light dependent resistor (LDR)s resistance changes with light intensity.
- Usually increasing light intensity decreases the resistance.
Making Input Transducers
Putting a thermistor (or an LDR) in a potentiometer instead of a variable resistor makes a simple input transducer (component that turns a variable into an electrical signal).
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LDR
- When the light intensity changes, the resistance of the LDR will change.
- The change in resistance of the LDR changes the potential difference across the resistor.
- This changing potential difference is the electrical signal produced.
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Thermistor
- When the temperature changes, the resistance of the thermistor will change.
- The change in resistance of the thermistor changes the potential difference across the resistor.
- This changing potential difference is the electrical signal produced.
Test yourself on Components
If a thermistor is connected in series with a resistor and battery, what will happen in the circuit when the temperature increases?
What effect will increased light intensity have on an LDR?
What is this the circuit symbol for?