Spreadsheet Assignment 1

Data Analysis: Thermistor

 

 

 

A circuit contains a thermistor and a resistor connected in series with a power supply of emf E volt and zero internal resistance. (see diagram below).

 

 

 

The thermistor can be placed in an environment (e.g. sand ) where its temperature can be changed. The thermistor’s electrical resistance changes with temperature in a non linear manner. The actual values of the resistance for different temperatures are found in dataAnalysisA2.xls (also found on the CD).

 

A screen dump of the excel spreadsheet is shown below. Please note that the second sheet (copy of data) is a backup copy of the resistance vs temperature values. This copy is given in case you lose the original data.

 

Note the following:

 

• Cell D4 contains the value of the emf, E of the power supply. When using it in formulae you would be advised to address it as $D$4 so that any scrolling of data always keeps an absolute reference to that cell.
• Cell J4 maintains the value of the electrical resistor R. Again you are better advised to reference this cell absolutely in any formula (i.e. $J$4 ).
• Columns B and C contain the data for thermistor’s electrical resistance and its temperature (in ^oC )
• Three columns are left blank for you to fill (columns E, F and G).

 

 

 

 

 

Activities:

 

1.      Write down a formula for the total current, I, flowing through the components using E, R and R_T.

2.      Use this formula to complete column E. For E, R and R_T use the appropriate cell references, remember that R_T is changing and you will need to be using values from column B.

3.      Write down a formula that will calculate the p.d. across the thermistor for each temperature, using I and R_T. Use this formula to complete the entries for column F.

4.      Write down a formula that will calculate the power dissipated by the thermistor at each temperature using I and V. Use this formula to complete the entries for column G.

5.      Produce a graph/chart that has temperature (on the x-axis) and Power (on the y-axis). Describe the shape of this graph as fully as you can using quantitative data as well as simple description.

6.      Produce a second graph which has power (on the y-axis) and electrical resistance of the thermistor (on the x-axis).

7.      Alter the values of E (in cell D4) and comment upon how the graphs change.

8.      Keeping the value of E constant, alter the value of R. Comment upon how the graphs are altered as R changes.

9.      Produce screen dumps of your results along with any comments you wish to make concerning the “maximum power” and the value of R.