Chapter 3 Voltage

2 Objectives –After completing this chapter, the student should be able to: Identify the six most common voltage sources. Describe six different methods of producing electricity. Define a cell and a battery. Describe the difference between primary and secondary cells.

3 Describe how cells and batteries are rated. Identify ways to connect cells or batteries to increase current or voltage output or both. Define voltage rise and voltage drop. Identify the two types of grounds associated with electrical circuits.

4 Voltage sources –Friction –Magnetism –Chemicals –Light –Heat –Pressure

5 Friction –Van de Graaf generator. Magnetism –Most common method of producing electrical energy. –Produced using a generator. –Powered by steam from nuclear power or coal, water, wind, or gasoline or diesel engines.

6 Direct current –Electrons flow in only one direction. Alternating current –Electrons flow in one direction, then in the opposite direction.

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8 Chemical –Cell –Second most popular method of producing electrical energy. –Consists of two metals: Copper Zinc –Many cells can be connected to form a battery.

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10 Light –Photovoltaic cell. –A single cell can produce a small voltage. –Many cells must be linked to produce a usable voltage and current. –Primarily used in satellites and cameras. –Cost is high, but is declining.

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12 Heat –Thermocouple –Two dissimilar wires twisted together. –Voltage is directly proportional to amount of heat applied. –Used in thermometers. –Also called a pyrometer.

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14 Pressure –Piezoelectric effect. –Voltage is small; must be amplified to be useful. –Used in crystal microphones, phonograph pickups (crystal cartridges), and precision oscillators.

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16 Battery –A combination of two or more cells. Primary cells –Cells that cannot be recharged. Leclanche cell or dry cell; also referred to as a carbon-zinc cell Alkaline cell Lithium cell

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20 Secondary cells –Cells that can be recharged. Lead-acid battery or wet cell. Nickel-Cadmium cell or Ni-Cad.

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22 Connecting Cells and Batteries –Series Series-aiding: –I T = I 1 = I 2 = I 3 (current) –E T = E 1 = E 2 = E (voltage) Series-opposing: –Little practical value

23 –Parallel Current expressed as I T = I 1 = I 2 = I 3 Voltage expressed as E T = E 1 = E 2 = E 3

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25 Voltage rise –Potential energy or voltage introduced into a circuit. Voltage drop –The energy given up as electrons encounter resistance in the circuit.

26 Ground –Earth Used to prevent electric shock. –Electrical Provides a common reference point.

27 In Summary –Current –Voltage –Voltage source Friction Magnetism Chemicals Light

28 Heat Pressure –Voltage rise –Voltage drop –Ground Earth Electrical