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Battery. A water current in a pipe is maintained by pressure. The pressure provides potential energy to move the water. A battery is a pump for electrons. Water Pump. v. D P. d. A. Different metals hold their electrons with different energies. Energy into potential
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A water current in a pipe is maintained by pressure. The pressure provides potential energy to move the water. A battery is a pump for electrons. Water Pump v DP d A
Different metals hold their electrons with different energies. Energy into potential Electron as test charge If two different metals can interact then they create an electric potential DV. Electromotive series The electrode potential (V) for several metals: Lithium -3.0 Aluminum -1.7 Zinc -0.76 Iron -0.44 Lead -0.13 Hydrogen 0.00 Copper +0.34 Silver +0.80 Gold +1.3 Chemical Energy
The ionic medium connecting the two metals is called an electrolyte. Must allow ions to move The chemical potential difference between copper and zinc in the cell at right is 1.1 V. Wet Cell
Chemical cells are called batteries. The lead acid car battery is a wet cell. Batteries that use a damp paste are called dry cells. Alkaline battery Dry Cell
EMF • The potential difference from a chemical cell battery has the historical name electromotive force. • EMF for short • Symbol E • The EMF is not a force. • Electric potential is not force. • The symbol for a battery is alternating long and short lines. • Long side is more positive potential + +
Ground • Electric potential has an arbitrary zero. • Potential difference matters to charges. • The earth’s surface is a useful reference point for potential, and is called ground. • The symbols for ground are downward triangles. • Can be with lines • Assumed to be 0 V
A conductive path is needed for current to flow. Connect positive to negative A complete path from positive to negative forms a circuit. A load is needed to prevent current from flowing too much. Stones in the pipe for water flow Complete Circuit I V load
The load can be an electric circuit or another conductor. Skin and flesh conduct poorly. Better than a true insulator The current may find a path to complete the circuit. Electric Shock next