current electricity. section 22.1 objectives describe conditions that create current in an electric...
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Electric Current I=ΔQ/ΔtTRANSCRIPT
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Current Electricity
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Section 22.1 ObjectivesDescribe conditions that create current in an
electric circuit.Use Ohm’s law to calculate properties of an
electric circuit.Differentiate between power and energy in
an electric circuit.
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Electric CurrentI=ΔQ/Δt
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Example ProblemsThe current in a light bulb is 0.835 A. How
long does it take for a total charge of 1.67 C to pass through the filament of the bulb?
A total charge of 9.0 mC passes through a cross-sectional area of a nichrome wire in 3.5 s. What is the current in the wire?
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ResistanceR = ΔV/IOhm’s law—the resistance is constant over a
wide range of applied potential differences
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ResistorsCan change current by changing the
potential difference across the ends of the conductorI = ΔV/R
How can the current change if the potential difference stays the same?
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Example ProblemsThe resistance of a steam iron is 19.0 Ω.
What is the current in the iron when it is connected across a potential difference of 120 V?
The current in a microwave oven is 6.25 A. If the resistance of the oven’s circuitry is 17.6 Ω, what is the potential difference across the oven?
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Sources of CurrentPotential difference
Batteries
Generators
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Electrical Components
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Section 22.2 ObjectivesExplain how electrical energy is converted
into thermal energy.Calculate the amount of power dissipated
through resistors.Calculate the amount of energy used in
kilowatt-hours.
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Electric PowerP = IΔV
Using Ohm’s law (ΔV = IR), we can express the power dissipated by a resistor by the following equations:P = I ΔV P = I2RP = (ΔV)2/R
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Example ProblemAn electric space heater is connected across a 120 V outlet. The heater dissipates 1320 W of power in the form of electromagnetic radiation and heat. Calculate the resistance of the heater.
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Example ProblemA 6.0 V battery delivers a 0.50 A of current to an electric motor connected across its terminals. What power is delivered to the motor?
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The Kilowatt-HourAmount of electric energy used by a device is
its rate of energy consumption (J/s) times the number of seconds (s) used
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Example ProblemAn electric space heater draws 15.0 A from a 120 V source. It is operated, on the average, for 5.0 h each day.
a) How much power does the heater use?b) How much energy in kWh does it
consume in 30 days?c) At $0.12 per kWh, how much does it
cost to operate the heater for 30 days?