Apparatus:
Thermistor, beak, tripod stand, boiling tube containing paraffin, spirit lamp, thermometer, voltmeter, ammeter, power supply and connect wires.
Theory:
Thermistor is a semiconductor whose resistance changes with temperature. Thermistor have negative temperature co-effect of resistance, thus their resistance decreases with the increase of temperature and vice versa. Highly temperature sensitive thermistors are used for temperature measurement.
Procedure:
1. Draw the circuit diagram and make the connection accordingly. Ammeter and power supply are connected in series with thermistor while voltmeter is connected parallel to it. a half degree thermistor is also fixed with thermistor and dipped into the boiling tube containing liquid paraffin.
2. Place a beaker, filled two third with water, on tripod stand. Dip the boiling tube containing thermistor into the water.
3. Switch on the power supply and note the temperature, reading of voltmeter and ammeter.
.Start heating the water in the beaker with spirit lamp. This increases the temperature of the thermastor gradually. Note the reading of voltmeter V and ammeter 1 after every 5oC rise in temperature.
5. Take at least six reading and find the resistance of thermistor at different temperature taking ratio V/I.
Observations & Calculations:
Result:
As resistance decrease with increase of temperature this shows the variation of the resistance of thermistor with temperature.
Precautions:
1. Thermistar should not touch with the walls of the boiling tube,
2. Use a very sensitive thermistor
3. Temperature should not increased beyond 70 °C.
Viva voce:
Q.1: What is thermistor?
Ans:Thermestor is a semi-conductor device which behaves as a thermal resistance.
Q.2. What is meant by negative temperature co-efficient of resistance?
Ans: When resistance decreases with increase in temperature then the temperature co-
efficient of resistance is negative.
Q.3: What is the use thermistor?
Ans: Thermistor are used in thermometer to measure the temperature and in fire alarm.
Q.4: What is the St unit of temperature co-efficient of resistance?
Ans: The St unit of temperature co-efficient of resistance is (K)
Q.5: How does the resistance of thermistor vary with temperature?
Ans: The resistance of thermistor decreases with rise in temperature and vice versa.
