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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Experiment: S
TUDY THR
V
ARIATION OF
R
ESISTANCE OF A
T
HERMISTER
WITH
T
EMPERATURE
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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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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