Investigating How the Resistance of a Thermistor Varies With Temperature

INVESTIGATING HOW THE RESISTANCE OF A WIRE VARIES WITH TEMPERATURE ADAN SHENNAN-FARPON

Equipment/materials required: 1) Ammeter

6) Wires

2) Voltmeter

7) Ther0mometer

3) Power Pack

8) Ice

4) Beaker

9) Clamp Stand

5) Bunsen Burner

Diagram Measuring: In my experiment, I need to measure how resistance changes with temperature in a wire. For measuring temperature, I shall be using a thermometer. The thermometer is graded to measure to the nearest degree, which allows me to get accurate readings. Its range is -5 C to 105 C, C, which is a ° 

° 

good range because it allows for a large amount of results. In order to measure resistance, I need to record the current and the voltage, as resistance = voltage/current. For measuring voltage, I will use a voltmeter, connected in parallel across the part of the wire that will be in the water bath. The range I will be working with is 2000 mV; therefore there is a precision of +-0.01 (?) volts. The reason why I chose this r ange is that the power pack can only supply a voltage of up to 12 V, so using a bigger range would be pointless. Also, this low range of voltages means the wires will not be heated excessively by a large current, a variable which would affect my experiment. I will be taking measurements of the resistance at 10 different temperatures, starting at around 0  C  C ° 

and repeating the measurements at intervals of about 10 C. C. Each measurement will be repeated 3 ° 

times for increased reliability by applying three different voltages to the circuit and seeing how the current changes, thus calculating resistance. The ammeter will be placed in series and the voltmeter will be placed in parallel. Also, I will be avoiding parallax error with the thermometer by not reading the temperatures at an angle to the thermometer.

Variables: In my experiment, I will be measuring how the resistance of the wire changes, so resistance is my dependant variable. I will be able to calculate the resistance because I will have values for current and voltage, and R=V/I. I will be changing the temperature as I go; therefore it is the independent variable.

The other main variable would be the equipment used, so I will use the same equipment throughout the experiment to avoid this control variable having any effect on my final results and to make my experiments a fair test. Also, the voltage I supply across the circuit will be kept quite low, below 2V, so as to avoid a large current having a heating effect on the wires which would change the resistance (I wish to avoid this so as to see the true effect of temperature on resistance). Repeat readings will also ensure my test is fair, as it will increase the reliability of my results by allowing me to identify anomalous results.

Safety: When conducting my experiment I will be dealing with very hot water, so I will handle the beaker with extra precaution. Also, a Bunsen flame will have to be lit, so I will take care with the fire and be safe around it by following all the safety guidelines.

Error: When conducting my experiment, the main source of error will be the fact that it would be impossible to know what temperature the wire is at exactly. Instead, I am measuring the temperature of the water bath it will sit in, however the temperature of the wire could be above or below this. There is no way available for me to measure the temperature of the wire directly except using a thermocouple, which I do not have access, and this could affect my results.

Method: 1) Set up circuit as shown in diagram below, starting with ice cold water (0 C) (cooled by placing ice ° 

cubes in it) 2) Record the voltage and current at each temperature up to about 100 C (heating the water using a ° 

Bunsen burner) 3) Apply three different voltages at each temperature, achieving 3 repeat readings for current and voltage of each temperature used. 4) By using the formula: Resistance= Voltage / Current, calculate the resistance at each temperature, then work out an average over the 3 readings, ignoring any anomalous results. 4) The data collected will be used to plot a graph of temperature versus resistance, which will show me the relationship between temperature and resistance in the wire, allowing me to provide a conclusive argument at the end of my experiment.