Science Notes → Circuits
Learning Intentions
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Calculate the effective resistance of a series or parallel circuit
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Explain the role of effective resistance in circuits
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Calculate the current and voltage across individual elements in series and parallel
circuits
Series Circuits
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Voltage is shared between all elements according to their resistance
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Current remains constant for elements in series
Parallel Circuits
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Each parallel branch receives the same amount of voltage
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Current splits at junctions so that the required amount flows through each branch
Effective Resistance
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The power source provides enough current for all connected elements to work as
predicted by Ohm’s Law
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Current splits at junctions but the total current moves through the battery
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Effective resistance is the resistance a single resistor would need to have the same
current flow through the battery as the overall circuit
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V = I x R → Voltage = Current x Resistance
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Series: RT = R1 + R2 + … + RN
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Parallel: 1/RT = 1/R1 + 1/R2 + … + 1/RN
Example 1
Calculate the effective resistance of the circuit
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RT = 30 + 45 = 75 ohms
How much voltage does the 45 A(amps) resistor use?
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I = V/RT = 12/75 = 0.16 A
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V = IR = 0.16 x 45 = 7.2 V
Terms & General Knowledge
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Ω → Ohms
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A → Amps
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V = I x R → Voltage = Current x Resistance
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Long bar (in battery) is positive charge
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Currents generally flow from positive to negative