13%20Electric%20Circuits

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13 Electric Circuits
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Chapter Outline
1 Electric Circuits and Electric Current 2
Ohms Law and Resistance 3 Series and Parallel
Circuits 4 Electric Energy and Power 5
Alternating currents and Household
Current Everyday Phenomenon The Hidden
Switch in Your Toaster
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Use of Voltmeter
Voltmeter is connected across the resistance.
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Use of Ammeter
Ammeter is inserted into the circuit to measure
current.
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Electrical Energy
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Electrical Energy and Power
Our daily life depends on electrical energy. We
use many electrical devices that transform
electrical energy into other forms of energy. For
example, a light bulb transforms electrical
energy into light and heat. Electrical devices
have various power requirements. Electrical
power, P is defined as the electrical energy
transfer per unit time,
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Electric Power
Since the electrical energy is charge times
voltage (QV), the above equation becomes,
Since the current is charge flow per unit time
(Q/t), the above equation becomes,
Since V IR, the above equation can also be
written as,
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Killowatt-hour (kWh)
The SI unit of power is watt, after James Watt
(1736-1819), who developed steam engines.
Utility companies use the unit kilowatt-hour to
measure the electrical energy used by customers.
One kilowatt-hour, kWh is the energy consumed for
one hour at a power rate of 1 kW.
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Exercises
1. State Ohms law in an equation form in terms
of voltage and current. 2. Define power in an
equation form in terms of voltage and current.
3. When an appliance is plugged in a 120-volt
outlet, it draws a current of 8 amperes.
Calculate the power of the appliance. 4. If the
above appliance is used 10 hours a day for 28
days per month, and if the cost of electricity is
12 cents per kilowatt-hour, how much does it cost
to operate the appliance for a year?
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Electrical Power Transmission
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AC adapter
INPUT AC 120 V, 60 Hz, 15 W OUTPUT DC 9V, 1A
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Alternating Current
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Alternating Voltage
Effective voltage 115 V
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Household Circuits
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Power and Current Ratings of some common
Appliances
Appliance Power (W) Current (A)
Stove 6000 (220V) 27
Clothes dryer 5400 (220V) 25
Water heater 4500 (220V) 20
Clothes washer 1200 10
Dishwasher 1200 10
Iron 1100 9
Coffeemaker 1000 8
TV 100 0.8
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Everyday Phenomenon
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Bimetallic Thermostat
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CP5