Download Series Circuit - E. R. Greenman

Series Circuit
Series
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Circuit in which current passes through all
resistors
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Only one path for current
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Each resistor uses up some of the potential
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Vsource = Va + Vb + ....
Resistance
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Equivalent resistance for devices in a series
circuit is sum of individual resistances
R = R1 + R 2 + R 3 + …
Current
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Current in a series circuit is the source voltage
divided by the equivalent resistance
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Current is the same everywhere in the circuit
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Icircuit = Vsource/Req
Example
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Two resistors, 47Ω and 82Ω, are connected in
series across a 45V battery. What is the
current in the circuit? What is the voltage drop
at each resistor?
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Known: R1=47Ω R2=82Ω V=45V
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Req = R1 + R2
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Req = 47Ω + 82Ω = 129Ω
Example Continued
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Current in the resistor: I = V/R
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I = 45V/129Ω = 0.349 A
Example Continued
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Will current increase, decrease or stay the
same if the 47Ω resistor is replaced by a 37Ω
resistor?

New Req = 37Ω + 82Ω = 119 Ω

I = V/R = 45V/119Ω = 0.378 A

Current increases
Parallel Circuits
Parallel Circuit
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
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Multiple pathways for current
Total current is the sum of the currents at each
resistor (Current is NOT the same everywhere)
Potential difference is the same everywhere in
the circuit
Parallel Circuit
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Placing resistors in parallel always decreases
the equivalent resistance of the circuit
BUT... This increases the current!
Symbols Used
Sample Circuits
Circuit A
Circuit B