·
Thermistor
- Resistance of thermistor decreases as temperature increases.
- Can be used as temperature sensors
In an electric circuit, the thermistor symbol looks like this:
Designing Experiments to Study the Relationship Between Temperature and Resistance of a Thermistor
- Place thermistor inside a beaker of water with a thermometer. The beaker of water acts as a water bath so that the temperature increases more gradually when heated and also helps to prevent the thermistor from getting heated directly.
- The thermistor should be connected to electrical circuit. Connect the ammeter in series and the voltmeter in parallel with the thermistor.
- At fixed temperature, read the values on the ammeter and voltmeter to get the current and voltage across the thermistor.
- Calculate the resistance at a specific temperature by using the equation R = V / I.
- Calculate the resistance for different temperatures (0°C ~ 100°C). For temperatures below room temperature, put ice in the beaker to lower the temperature. For temperatures above room temperature, heat up the water in the beaker.
- For each temperature, repeat the experiment a few times and get the average.
If you plot the resistance-temperature graph, it will look something like this...
Light-Dependent Resistor
- Resistance of LDR decreases as light intensity increases.
- Can be used in street lamps
The LDR symbol looks like this in an electric circuit:
Designing Experiments to Study the Relationship Between Light Intensity and Resistance of LDR
- Place LDR so that light can be shone through a circular hole in the black card.
- The LDR should be connected to electrical circuit. Connect the ammeter in series and the voltmeter in parallel with the LDR.
- At a fixed hole size, read the values on the ammeter and voltmeter to get the current and voltage across the LDR.
- Calculate the resistance at a specific hole size by using the equation R = V / I.
- Calculate the resistance for different hole sizes. The larger the hole size, the larger the light intensity. Keep the distance between the LDR and black card constant.
- For each light intensity, repeat the experiment a few times and get the average.
If you plot the resistance-light intensity graph, it will look like this:
