Transcript Electric Circuits

Electric Circuits
Objectives
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Distinguish between series and parallel
connections
Calculate the current, voltage, and
equivalent resistance for devices
connected in series and parallel
Construct a voltage divider
Describe the features of a multi-meter
and explain how to use it in a circuit
Electric Circuit Components
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Capacitor
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Stores charge
Creates a potential difference
Source of energy
Resistor
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“Opposes” current (charge flow)
“Uses” potential difference
Dissipates energy
Electric Circuits
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Electric current requires
two conditions
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A “closed” circuit, or
complete path for charges
to flow
A potential difference, or
voltage source (usually a
cell or battery)
Electric Circuits
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Two types of electric circuits
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Series (only one current path)
Parallel (more than one current path, i.e.
“branches”)
Equivalent Resistance
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Series resistors
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Resistors in series add together
Req  R1  R2  R3  Rn
Current
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The current through a circuit
component is equal to the voltage
divided by the resistance
V
V
R I 
I
R
Textbook, Pg. 533
Voltage
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The voltage “drop” or potential
difference across a circuit component
equals the product of the current and
the resistance
V
R   V  IR
I
Textbook, Pg. 534
Voltage Divider
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Series circuit used
to produce a
voltage source of
desired magnitude
from a highervoltage battery
Textbook, Pg. 535
Practice Problems
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Textbook, Page 534 #1 – 5
Textbook, Page 536 – 537 (Examples)
Textbook, Page 537 #6 – 9
Equivalent Resistance
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Parallel resistors
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Resistors in parallel
add together as the
reciprocals
1
1
1
1
1
 
 
Req R1 R2 R3
Rn
Hint: Remember to invert the sum to find Req
Textbook, Pg. 539
Kirchoff’s Laws
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Voltage
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Conservation of
energy
Current
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Conservation of
charge
Conservation of Energy
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The sum of potential “drops” or
voltages in a circuit equals the source
In a series circuit, all the voltages add
up to equal the source
In a parallel circuit, the voltage applied
to each branch is equal to the source
Conservation of Charge
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The sum of all currents in a circuit is
equal to the current leaving the source
In a series circuit, the current is the
same at every point
In a parallel circuit, the sum of all
currents entering any junction is the
same as the sum of all currents leaving
the junction
Series-Parallel Circuit
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What is the voltage drop across each
resistor and the current flowing through
them?
Practice Problems
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Textbook, Page 540 #10 – 12
Textbook, Page 547 #13
Measurements
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Voltmeter
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Ammeter
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Measures current (amps)
Galvanometer (very sensitive ammeter)
Ohm-meter
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Measures potential difference (volts)
DVM (digital voltmeter)
Measures resistance (ohms)
Multimeter
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Measures all three
Measurements
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Voltmeter
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Ammeter
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Parallel
Series
Ohm-meter
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Disconnect power
Isolate resistor
from circuit
Textbook, Pg. 547