AP Physics 2 Lab – EMF & Internal Resistance

The goal is to determine experimental values for the emf and internal resistance of the 3.0 V battery in the Vernier circuit board.  Note that 3.0 volts is a “nominal value” and the actual emf of the battery may be different!  This exercise also provides practice analyzing data and employing graphical analysis.

Record of the Experiment:

1. Create a well-labeled schematic diagram using standard symbols illustrating the basic circuit setup used for this experiment.  The schematic should include the voltmeter!

2. Produce a well-labeled data table showing columns for external resistance and terminal voltage. Leave room for three additional columns explained below.

Method 1:  Statistical and Algebraic Analysis

1. Derive an expression for the terminal voltage V in terms of the internal resistance, r, the emf, ℇ, and the external resistance R.  Show your work!

2. Based on the expression, when R = 22 kΩ the terminal voltage should be essentially the same as the emf.  Explain why this is so.

3. Now rearrange the expression and solve for the internal resistance, r, in terms of the emf, ℇ, the terminal voltage V, and the external resistance R.  Show your work!

4. Use the expression and the apparent emf found when R = 22 kΩ to calculate the internal resistance for each trial.  Include a column in the data table to show these results. 

5. Determine the mean value and mean or standard deviation in the value for the internal resistance.

Method 2:  Graphical Analysis – Linearization of Data

1. Calculate decimal values for the reciprocal of the external resistance and the reciprocal of the terminal voltage.  Include columns for each of these quantities in the table.

2. Produce a large, high quality, scientific graph of reciprocal voltage versus reciprocal resistance.  Determine the line of best fit, including equation and correlation coefficient, shown on the graph.

3. Using the coefficients from the equation of the line, determine the emf and the internal resistance of the battery.  Show your work and/or explain!

Completed report

o Schematic diagram of lab setup

o Table with data and calculated values

o Method 1 work and results

o Method 2 graph and results