Group 30 Electrical System—VNL, VNM
Design and Function
Series/Parallel Circuits
A series/parallel circuit consists of some components
in series and others are in parallel. In the figure the
components side by side are in series since there is only
one current path. The two circuits above and below each
other are in parallel since there are two current paths.
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Typical Series/Parallel Circuit
Ohm’s Law in series/parallel circuits
In series/parallel circuits, the easiest way to find a device
value is to look at each part of the circuit separately.
For the example below, first find the resistance in each
branch. The two 2
and 4
resistors add to give a
resistance of 6
for this part of the circuit. For the other
2 resistors, 2
+ 1
= 3
.
To simplify the circuit, think of it as a parallel circuit having
a 6
and 3
resistor.
So, (6
x 3
)
4
(6
+ 3
) = 18
4
9
= 2
total
resistance.
The total circuit current, therefore, is:
I = V
4
R
I = 12 volts
4
2
= 6 amps
The current through each branch can also be determined.
For the branch of the circuit with the 6
total resistance:
I = 12 volts
4
6
= 2 amps
So, for each resistor in this branch, the voltage drop is
found as follows:
V = I x R
For the 2
resistor,
V = 2 amps x 2
= 4 volts
For the 4
resistor,
V = 2 amps x 4
= 8 volts
The sum of the voltage drops in a series circuit equals the
source voltage, so 4 volts + 8 volts = 12 volts.
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