Internal Resistance and EMF
A simple cell may be created by inserting zinc and copper electrodes into an ordinary potato. Such cells can be used to power low current appliances such as clocks and calculators. The video below demonstrates a short experiment using such a cell. Multimeters are used to measure the potential difference across and current through the cell. The current is adjusted by altering the setting of a load resistance connected to the cell. Measurements of the potential difference and current may be taken and used to calculated the EMF and Internal Resistance of the cell.