The parallel circuit rules show how to use Ohm's law when
the circuit has more than one device receiving electrical energy. It
will also help us see how the resistance, the current, and the voltage
change in the parallel circuit. A parallel circuit is shown below.
Notice that the circuit has 2 switches (green), 1 voltage source of 24
volts, and 2 resistors.
In a parallel circuit, the current has more than 1 pathway.
To be more precise, the circuit has 2 pathways or 2 branches.
Simply put, the current has the ability to "make choices" as to where it would go. If the current can either go this way or that way, then the circuit is a parallel circuit.
Look carefully at the circuit below and you will see that the current can either go to the 8 Ohms resistor or the 4 Ohms resistor. This is what we mean by "making choices."
Take a close look at the two red dots. Did you notice that both devices
are connected to the same two red dots? This means that both devices are
fed by the same voltage of 24 volts.
Rule #1: Devices in parallel circuits have the same voltage as the voltage source.
Now, let us talk about the current. Let us pretend that the resistance is the same in both branches.
Since there is a resistance, the current going there will be less.
Since the resistance is the same for both branches, it makes sense to say that both branches will receive the same amount of current.
The current I is split into I_{1} and I_{2}. Half of the current will go to the branch with the 4 Ohms resistor and the other half to the branch with the 4 Ohms resistor.Rule #2: In parallel circuit, the current in the circuit is equal to the the sum of the currents in its parallel branches.
Rule #3:
1
R_{p}

=
1
R_{1}

+
1
R_{2}

1
R_{p}

=
1
R_{1}

+
1
R_{2}

The parallel circuit rules can be summarized and generalized as below
Let V be the voltage feeding the circuit
1
R_{p}

=
1
R_{1}

+
1
R_{2}
+ ...

+
1
R_{n}

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Take the parallel circuits quiz below to see how well you understand
parallel circuits. After completing this quiz with 100% accuracy, you
will know exactly how the current, the voltage, and the resistors behave
in a parallel circuit. You will not need to use a paper and pencil to
complete this quiz.
First, read the lesson about parallel circuits and then take this quiz.
Objective of the parallel circuit quiz:
Test your knowledge with the quiz below: 
Nov 18, 20 01:20 PM
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