1. SERIES-PARALLEL COMBINATION CIRCUITS
USES A SERIES OF EQUIVALENT RESISTANCES TO SOLVE FOR THE TOTAL RESISTANCE IN A CIRCUIT

2. Always start with resistors farthest from the voltage source.
Look over circuit to see
how resistors are
placed in the circuit.
R2 and R3 are in parallel
with each other.
This combination
is in series with R1

3. EX: Two 12Ω resistors are connected in parallel and placed in series with a 6Ω resistor. The total voltage supplied to the circuit is 120V. Draw and label the circuit.
= 6Ω
=12Ω
VT=120V
=12Ω

4. b) Find the total resistance and total current in the circuit.
RT = R1 + Req
RT = 6Ω + 6Ω
RT = 12Ω
RT = VT/ IT
12Ω = 120V/ IT
IT = 10 Amps
1/Req= 1/12Ω + 1/12Ω
1/Req = 2/12
Req = 6Ω
R1=6Ω
Req= 6Ω

5. c) Find V1 V3 and I3. R1= V1 / I1 V2 =V3 = VT – V1
6Ω = V1/ 10 Amps V2 =V3 = 120V-60V
V1 = 60V V2 =V3 = 60V
R3 = V3/ I3
12Ω = 60V/ I3
I3 = 5 Amps

6. I1=10 Amps
V1=60V
=6Ω
IT=10Amps
I3=5A
I2=5Amps
VT=120V
=12Ω =
V2 = 60V
12Ω
V3=60V

7. 4.0 15 10 1.0 V= 9V Find the total resistance of the circuit.
If the battery is 9.0V, what is the total current in the circuit?
What is the current in R2 and R5?