Thermistor Experiment-Physics-Lab Mannual, Exercises for Physics. Allahabad University

Physics

Description: This is lab manual for Physics course. It was designed by Sakash Jashith at Allahabad University. It includes: Variation, Resistance, Thermister, Temperature, Negative, Coefficient, Heating, Arrangement, Boiled
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© Javaid Khurshid, PIEAS Page 1 of 2

Experiment: STUDY THR VARIATION OF RESISTANCE OF A THERMISTER” WITH TEMPERATURE

Object: To study the effect of temperature (max. of 100 °C) on a thermistor (negative

temperature coefficient).

Ref[http://tap.iop.org/electricity/resistance/110/page_45969.html]

Apparatus:

• A given thermistor (negative temperature, coefficient)

• Power supply, 5 V, DC

• Ohmmeter

• Mercury thermometer (-10C to +110 C)

• Beaker (250 ml)

• Heating arrangement

• Stand

Formula: No formula is used Procedure:

i) Clean all the terminals of wires with sandpaper. ii) Make connections as shown in the figure iii) Dip only the thermistor in a beaker containing normal cold water having

thermometer in it. iv) Supply power to the circuit v) Take readings of temperature and resistance. vi) Place a heating source below the beaker. vii) Now slowly heat the water and note down the current in it corresponding

to changing temperatures ‘T’ (say 10, 20, 30… °C) in regular steps. viii) Finally, measure the resistance of the thermistor at 100°C when water

gets boiled. ix) Plot a graph by placing temperature “T” (°C) on X-axis and Resistance“R”

(ohms) on Y-axis.

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© Javaid Khurshid, PIEAS Page 2 of 2

Observations: Take approximately 30 readings of different temperatures.

No. of obser- vation

Thermistor temperature T

Resistance R (ohms)

Result: Resistance of a thermistor decreases/increase with the increase in temperature.

Precautions:

• Connection must be tight.

• The points of contact of terminals should not add any insulting part of wires.

• The initial temperature and final temperature of thermistor must be measured accurately.

• The connecting wire of thermistor must be long enough in order to enable the thermistor to dip thoroughly in the water.

• The heating arrangement must be kept at a suitable distance away from the rest of the circuit.

• Heating must be done slowly.

Some Questions? • If the data is plotted on excel and interpolated, What will be the trend (linear, logarithmic,

polynomial, power, or exponential) for the highest R 2 value?

• If a thermistor is placed in an electrical circuit with constant DC voltage applied, what would be the effect of current through the circuit if the thermistor was heated up?

• What do you say about the material of a thermistor (Is it ohmic) ?

• When the thermistor is more sensistive to temperature variation?

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