Investigating The Resistance Of Thermistors and LDRs
Part 1A – The Thermistor And Changing Temperature
Aim: To investigate the effect that a change in temperature has on the resistance of a thermistor.
Equipment: • 1 x thermistor
(Dick Smith Electronics Cat No. R1895)
• connecting Wires
(banana plug & alligator clip at either end)
• hotplate • 500 mL Beaker
• blu-tack • Thermometer (-5oC to 110oC)
Your teacher will have already attached the thermistor to some long connecting wires and wrapped its exposed metal pins with blu-tack in order to create a waterproof barrier. Otherwise your multimeter will be measuring the resistance of the water not the thermistor!
Using A Multimeter
Caution: Do not use the multimeter to measure the resistance of a load in a circuit whilst the circuit is ‘live’. You risk damaging the multimeter if you do. Instead remove the load from the circuit and measure its resistance using the Ohms (Ω) scale on your multimeter.
Method: Set up your equipment as shown in the diagram above.
Step 1 Fill the beaker with about 400 mL of chilled water and place the thermometer into the water and measure its temperature.
Step 2 Place the thermistor into the beaker of water. Do not let it touch the glass walls of the beaker and make sure that its leads do not touch the hotplate. Wait 5 minutes before you start taking results. (Why do you need to wait 5 minutes?)
Step 3 Connect the multimeter across the ends of the wires attached to the thermistor.
Step 4 Turn the multimeter to the ohms (Ω) setting and record the thermistor’s resistance and the starting temperature of the chilled water with the thermometer.
Step 5 Turn the hotplate to high and record the thermistor’s resistance at 10oC intervals up to and including the boiling point. You only need to record your answers to the nearest kΩ.
Results: • Enter your data into an appropriately labelled results table.
• Plot a graph of the...