# Parallel Connection & Series Connection Description

An electric circuit can be divided into a series connection or parallel connection, depending on how the electrical devices are connected.
1. Series connection
With this method, multiple electric devices are connected serially with a single electric wire.
Figure represents a series connection in the form of a water flow.
The uniqueness of this water flow is that an equal volume of water flows through each of these waterfalls, which is also equal to the volume of water that flows from the source.
(I0 = I1 = I2 = I3)
Moreover, the sum of the height of the three individual waterfalls equals the height of the entire waterfall.
(V0 = V1 + V2 + V3)
2. Parallel connection
With this method, multiple electric devices are connected to a single electric wire.
Figure represents a parallel connection in the form of water flowing.
All the waterfalls have the same height.
(V0 = V1 + V2 + V3)
Moreover, the sum of the volume of the water that flows through the waterfalls is equal to the total volume of water.
(I0 = I1 = I2 = I3)

Resistance

1. Resistance of a series circuit
The combined resistance of the entire circuit is equal to the sum of the resistors in the circuit.
R0= R1 + R2 + R3

2. Resistance of a parallel circuit
The combined resistance of the entire circuit can be calculated with the following formula:
R0 = 1 / (1 / R1 + 1 / R2 + 1 / R3)
R0 is smaller than the smallest one between R1, R2, and R3

Current

1. Amperage of a series circuit
The amperage that flows through each of the electrical devices in the circuit is the same as for any other electrical device in the entire circuit.
I0 = I1 = I2 =I3

2. Amperage of a parallel circuit
The sum of the amperage that flows through the electrical devices in the circuit is equal to the amperage of the power supply.
I0 = I1+ I2 + I3

Voltage

1. Voltage of a series circuit
The sum of the voltage drops that occur with each of the electrical devices in the circuit is equal to the voltage of the power supply.
V0 = V1 + V2 + V3

Voltage
Voltage drop
While a current flows through a circuit, its voltage decreases each time it passes a resistor.
This decrease is called a voltage drop.
In the series circuit shown on the left, the power source has 12 V. The voltage that drops each time the current passes through a resistor can be calculated with the following formula:
Voltage drop when the current flows through 2 Ω resistor:
12 V x 2 Ω / ( 2 Ω + 4 Ω + 6 Ω) = 2V
Voltage drop when the current flows through 4 Ω resistor:
12 V x 4 Ω / ( 2 Ω+ 4 Ω+ 6 Ω) = 4V
Voltage drop when the current flows through 6 Ω resistor:
12 V x 6 Ω / ( 2 Ω+ 4 Ω+ 6 Ω) = 6V

2. Voltage of a parallel circuit
The voltage drop that occurs at each electrical device in the circuit is the same as any other electrical device, as well as the voltage of the entire circuit.
V0 = V1 = V2 = V3