How to Calculate the Voltage in a Series & a Parallel Circuit
Calculating voltages in a series circuit is a relatively simple process and it does involve having an understanding of some simple algebraic operations. Calculating voltages in a DC (Direct Current) circuits made up of pure resistance is easy. Calculating voltages in AC (Alternating Current) circuits involve calculating circuit impedance, which is the sum of the DC resistance and reactance. Calculating inductive and capacitive reactance can be a little tricky. Voltages in a simple parallel circuit, circuits where there is only one load in each parallel leg, always equals the source voltage, so there are no calculations necessary. Does this Spark an idea?
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Things You'll Need
- Paper
- Pencil
- Scientific calculator
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Instructions
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Calculating voltages in a DC series circuit
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1
Calculate the total circuit resistance by adding the individual resistances together. Rt = R1 + R2 + R3 + ... Rinf
Rt = Total Resistance in Ohms
R1 = Resistance of first resistor
R2 = Resistance of second resistor
R3 = Resistance of third resistor
Rinf = Resistance of any other resistors in the series circuit -
2
Calculate the total current flowing in the circuit. Total current flowing in a series circuit equals the applied circuit voltage divided by the total circuit resistance: I total = E/Rt
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3
Calculate the individual voltage drops across each resistor by multiplying the resistance (in ohms) of that resistor by the total current flowing in the circuit: Er = (It)R
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4
The sum of the individual voltage drops should equal the source voltage, the voltage applied across the circuit. These same steps apply to AC circuits that have only pure resistances in them.
Calculating voltages in an AC circuit having reactive components.
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5
Calculat voltages in an AC circuit having reactive components. Calculate the inductive reactance in Ohms: X l = 2(Pi)(F)(L). Inductive reactance in ohms is equal to two times the frequency in Hertz times the inductance in henries.
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6
Calculate capacitive reactance: X c = 1/2[(Pi)(F)c]. Capacitive reactance in ohms is equal to the reciprocal of two times pi times the frequency in Hertz times the capacitance in farads.
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7
The total impedance of an AC series circuit is equal to the sum of the impedances. Z t = Z r + Z X-C + Z XL where:
Z t = Total impedance in ohms
Z r = Total resistance of all pure resistances in the circuit
Z xc = Total capacitive reactance
Z xl = Total inductive reactance -
8
Calculate the total circuit current: I t = E/Z t
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9
Calculate the individual voltage drops by multiplying the total current by the individual impedances in ohms.
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Tips & Warnings
These calculations work for a series circuit because the current flowing in a series circuit is the same at every point in the circuit.
