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CIRCUITS AND RESISTANCE
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RECALL:
Current Potential Difference
DefinitionThe flow of electrons Causes electrons to
flow
Symbol I V
Units Amps (A) Volts (V)
Formula(if applicable)
I = Q t
V = E Q
How measured(if applicable) Ammeter Voltmeter
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Circuits:
A circuit is made up of a power supply, connecting wires & various elements that allow electrons to leave a power source, travel through the elements & return back to the power source.
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Common Electric Symbols
Battery/Power Source
Bulb
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Common symbols (cont’d)
Switch
Push-button Switch
Resistor
Voltmeter
Ammeter
V
A
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Circuits
Power Supply
Resistor
A
Ammeter
v
Voltmeter
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Types of Circuits:
There are 2 types of circuits: 1. Series Circuit 2. Parallel Circuit
SERIES
Trick to help identify type of circuit:
Series: Pen follows wire
Parallel: Pen can go in more than one direction
PARALLEL
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Series or Parallel?
AA
SERIES
SERIES
PARALLEL
PARALLEL1.
4.3.
2.
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Symbol: RUnits: Ohms, Ω Resistance
Resistance is how difficult it is for current to flow
• A device with HIGH Resistance will have very little current passing through it
• A device with low resistance will have a large current passing through it
A resistor is used to slow current down
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IF:R is High than I is lowR is Low than I is high
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Equivalent Resistance - Req
Equivalent Resistance is the TOTAL resistance of a circuit Symbol: Req Units: Ohms = Ω
Formulae:
Series:
Req = R1 + R2 + R3 + …
Parallel:
...3
1
2
1
1
1
Re
1
RRRq
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5
3 10
Type of circuit: Series
Formula: Req = R1 + R2 + R3
Req = 10 + 5 + 3
Req = 18
What is the equivalent resistance (Req) of the circuit below?
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30
75
Type of circuit: Series
Formula: Req = R1 + R2
Req = 75 +30
Req = 105
What is the equivalent resistance (Req) of the circuit below?
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Type of circuit: Parallel
Formula:
What is the equivalent resistance (Req) of the circuit below?
10 Ω
15 Ω
21
11
Re
1
RRq
1 ÷ 0.1666 = 6Ω
15
1
10
1
Re
1
q
0666.01.0Re
1
q
1666.0Re
1
q
6Req
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Type of circuit: Parallel
Formula:
What is the equivalent resistance (Req) of the circuit below?
321
111
Re
1
RRRq
1 ÷ 0.3333 = 3Ω
15
1
5
1
15
1
Re
1
q
0666.02.00666.0Re
1
q
3333.0Re
1
q
3Req
15
5
15
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KEY POINTS
321 R1
R1
R1
Req1
Symbols of circuit parts: Voltmeter, Ammeter, Power Supply, Resistor
Two types of circuits (series and parallel)
Formula for Req (equivalent resistance)
Series – Req = R1 + R2 + R3
Parallel -
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RECALL:
Resistance Current Potential Difference
DefinitionSlows current
downThe flow of electrons
Causes electrons to flow
Symbol R I V
Units Ohms (Ω) Amps (A) Volts (V)
Formula(if applicable)
R = V I
I = Q t
V = E Q
How measured(if applicable) Calculated Ammeter Voltmeter