Physics Coursework

The effect of temperature on the resistance of a thermistor

Aim: The aim of this experiment is to find out whether temperature affects the resistance of a thermistor.

Variables:

• The temperature.

• Type of ammeter.

I will be investigating whether or not a change in temperature of water to find out whether or not it will affect the resistance of a thermistor.

I will be keeping the following variable the same:

• The power supply.

I will be taking readings of the temperature, volts, amps and resistance. I will be using a digital voltmeter, ammeter and thermometer for more accurate results. I will also be repeating the experiment at least twice and getting an average. I will be measuring and recording my results in amps, volts, resistance and degrees Celsius.

Apparatus:

Stand

Ammeter

Bunsen burner

Voltmeter

Thermistor

Thermometer

Beaker

Tripod

Power pack

Electric leads

Diagrams:

This diagram shows the electrical circuit involved:

This diagram shows the apparatus set up:

Definitions:

 Current- This is a measure of the flow of electrons around a circuit (measured in Amperes or Amps (A))

Voltage-

I predict that the graph will look something like this:

Explanation of prediction:

In my prediction I have stated that a change in temperature will affect the resistance of the thermistor.

In general an increase in temperature increases the resistance of metal but decreases the resistance of semiconductors. The resistance of most thermistors decrease as their temperature rises. In my case the resistance theoretically will in fact decrease as I raise the temperature.

The electrons in the heat energy produce resistance in the electrical circuits. We can measure ho w many electrons have effected the thermistor by measuring the current and the voltage.

Scientific theory

The current and voltage of an electric circuit, is given by the formula V=IR. This is known as Ohms. Ohm´s Law is only applicable, when the temperature of the resistor is kept constant. Therefore Ohms law is only applicable to Ohmic conductors. Examples of Ohmic conductors are metals and alloys at constant temperatures. Anything that doesn’t obey Ohms law, are know as non-Ohmic Conductors.

My prediction says that the resistance will decrease with an increase of temperature I can now verify that with the help of my results and graph.

Evaluation:

In all I think my experiment was very successful.  I did not run into any difficulties except for one minor problem. This problem was not picked up in my preliminary experiment but was a factor that affected my main experiment. This problem was that the volt meter was dysfunctional at the temperature of 80 degrees or above.  The results I obtained were all of a good quality.  I believe they are of good quality as I had just one result that showed up to be out of place.  All of the other readings again correspond to my prediction and analysis.  The one odd result was probably due to an inaccurate reading of the ammeter or the voltmeter.  Although I feel that my experiment was successful if I were to do it again I would change one or two things. One of these things would be repeating the experiment at least five times and finding averages.