chapter 3 voltage. 2 objectives –after completing this chapter, the student should be able to:...
TRANSCRIPT
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.
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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