1. Draw a potential divider circuit where the output potential difference increases as the temperature of a thermistor increases. Hint:
As temp of thermistor increases, what happens to its value of resistance?
Therefore what happens to the potential difference across it?
Therefore where should you connect the output circuit (voltmeter in our case)?

2. A thermistor has a resistance of 20kΩ at 30◦C and 200Ω at 60◦C
A thermistor has a resistance of 20kΩ at 30◦C and 200Ω at 60◦C. The thermistor is connected as a potential divider with a 100 Ω resistor.
a) Draw the circuit
b) If the emf is 12V, what is the output potential difference across the fixed resistor at:
i) 30◦C
ii) 60◦C?
0.060V
4.0V

3. Thermistors as thermometers
26/06/2018
LO:
Be able to use the potential divider equation to calculate expected potential differences at different temperatures.
Measure body temp using thermistor

4. If you were to use your thermistor in a potential divider circuit, what would a good value for the fixed resistor?
-Hint think what would happen to the pd if the fixed resistor was very large or very small?

5. Use your graph to calculate the value of resistance you would expect at 18C, 20C, 22C,24C. Then 30C, 32C, 34C, 36C 38C.
Temperature (oC)
Resistance (Ω)
PD across fixed resistor (V) 18 20
etc

6. Now, using your chosen value of fixed resistor, calculate the potential difference you would expect across the fixed resistor for each of the above.
Measure your input pd from your cell first.

7. Make your potential divider circuit.
Measure the potential difference across the fixed resistor.
What is the temperature in the room?
Use the same method to determine your body temperature.
3) What would you expect to happen to the pd if you were to take your circuit outside? Try it!
Extension – How could the circuit be modified so that the output voltage range & values remain the same but at different temperatures?
Use a variable resistor instead of a fixed resistor

8. A thermistor has a resistance of 10kΩ at 5oC and 200Ω at 50oC
A thermistor has a resistance of 10kΩ at 5oC and 200Ω at 50oC. It is connected in series with a resistor of value 1000Ω and a 20V power supply.
Draw the circuit
Calculate the output voltages across the fixed resistor when the thermistor is at i) 5oC and then at ii)50oC bi) 1.82V bii) 16.7V
Calculate the current in the circuit when the thermistor is i) 5oC and ii) 50oC
ci) 1.8x10-3A cii) 0.017A

9. Practice:
Jan 2010 Past Paper qu3
Qu4 & 5 pg133
Questions from last time:
Qu 5 Pg 129
Qu2a & 2b pg 132
Qu6 Pg 129 (Extension)
Qu 2 & 4 Pg 131 (Extension)