Chapter 3

Voltage

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• 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.

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• 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.

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

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• 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.

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• Direct current– Electrons flow in only one direction.

• Alternating current– Electrons flow in one direction, then in the opposite

direction.

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• 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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• 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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• 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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• 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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• 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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• Secondary cells– Cells that can be recharged.

• Lead-acid battery or wet cell.

• Nickel-Cadmium cell or Ni-Cad.

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• Connecting Cells and Batteries– Series

• Series-aiding:– IT = I1 = I2 = I3 (current)

– ET = E1 = E2 = E (voltage)

• Series-opposing:– Little practical value

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– Parallel• Current expressed as IT = I1 = I2 = I3

• Voltage expressed as ET = E1 = E2 = E3

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• Voltage rise– Potential energy or voltage introduced into a

circuit.

• Voltage drop– The energy given up as electrons encounter

resistance in the circuit.

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• Ground– Earth

• Used to prevent electric shock.

– Electrical• Provides a common reference point.

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• In Summary– Current– Voltage– Voltage source

• Friction• Magnetism• Chemicals• Light

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• Heat

• Pressure

– Voltage rise– Voltage drop– Ground

• Earth

• Electrical