1. Series vs Parallel Circuits

2. Both with a 12V battery and 3 lights with 5 ohms of resistance
Series
Parallel

3. Voltage in Circuits
In a series circuit, voltage is shared throughout the circuit.
VT = V1 + V2 + V3 + … + Vn
In a parallel circuit, voltage is the same everywhere in the circuit.
VT = V1 = V2 = V3 … = Vn

4. Series
Parallel

5. Current in Circuits
In a series circuit, current is the same everywhere. This is because there is only one path for the electricity to flow through.
IT = I1 = I2 = I3=…= In
In a parallel circuit, the current that leaves the battery is divided by each path, with paths that have less resistance having more current.
IT = I1 + I2 + I3+…+ In

6. Resistance in Circuits
In a series circuit, the total resistance is the sum of all of the resistances added together.
RT = R1 + R2 + R3 + … + Rn
In a parallel circuit, the total resistance is the sum of the reciprocals of the resistance.
1/RT = 1/R1 + 1/R2 + 1/R3 + … 1/Rn
(Careful when solving for this. Remember, you are solving for RT , not 1/RT)

7. Summary of Formulas Series Circuit Parallel Circuit Voltage
VT = V1 + V2 + V3 + … + Vn
VT = V1 = V2 = V3 = … = Vn
Current
IT = I1 = I2 = I3=…= In
IT = I1 + I2 + I3+…+ In
Resistance
RT = R1 + R2 + R3 + … + Rn
1/RT = 1/R1 + 1/R2 + 1/R3 + … 1/Rn

8. Sample Question – Series Circuit

9. Sample Question – Parallel Circuit Calculate R3 and the current through the 12 ohm resistor

10. Practice problems are posted on the website!