= Battery voltage measurement experiment
The institutional handout <Measurement of Emf Using a Potentiometer, Oklahoma Christian University laboratory> (Experimental Activity: calibration procedure, measuring a test cell, and measuring internal resistance of a cell) compares unloaded and loaded <battery> readings. Its apparatus uses a slidewire <potentiometer>, calibrated resistance coils, a reference cell, a <galvanometer>, a nominal $1.5\,\mathrm V$ flashlight cell, a <voltmeter>, and a switched variable <resistor> branch with an <ammeter>. Calibration uses the reference cell's tagged <electromotive force>; zero <galvanometer> deflection establishes a <null measurement>. With the load branch open, the null reading draws no test-cell <electric current>. The protocol compares newer and older cells using both instruments, then records simultaneous loaded terminal <electric potential difference> and <electric current>. It prescribes brief measurements, opening the load switch between readings, and periodic calibration rechecks. These are documented procedures, not run data.<Measurement of Emf Using a Potentiometer, Oklahoma Christian University laboratory>[Experimental Activity, calibration procedure and measuring a test cell; measuring internal resistance, side branch K-A-R and simultaneous readings]{ref}
For the <battery internal resistance> model, $V_L=\mathcal E-rI$. The handout's analysis estimates <electromotive force> from the intercept and $r$ from the negative slope, then compares the intercept with the independent null reading.<Measurement of Emf Using a Potentiometer, Oklahoma Christian University laboratory>[Measuring internal resistance of a cell, final analysis paragraphs: line intercept/slope and comparison with the earlier emf measurement]{ref}
Additional replication controls are to repeat the open-load reading after the sweep, return to an earlier load setting to detect drift, and record <temperature>, elapsed time, instrument resolution and <measurement error>. Include <ammeter> and contact <electrical resistance> in the external path; allow for <voltmeter loading> if a <voltmeter> replaces the null instrument. The <Thévenin measurement experiment> gives the corresponding meter-loading correction. Curvature or time-dependent readings can reject the constant-$r$ approximation, but a terminal curve alone does not identify which internal transport or <electrode> process caused the deviation. These extra controls and interpretations are model-based extensions, not reported outcomes of the handout.
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