Basic of Electrical Circuit


Voltage and current

The speed of the waterwheel changes by changing the water volume in the tank. This means that the speed of the water flowing to the waterwheel changes with the change in the water pressure in the tank.
When this phenomenon of water is substituted with electricity, the water volume (water pressure) is the voltage, and the water flow is the electrical current.

Current and resistance
The force of the water flow changes with the height of the gate that is located between the tank and the waterwheel. As a result, the speed of the waterwheel changes.
This gate is equivalent to the resistance in an electrical circuit.

Current, voltage, and resistance
Increasing the water volume in the tank increases the speed of the waterwheel. On the other hand, lowering the gate to oppose the water flow decreases the speed of the waterwheel. Thus, it is possible to operate the waterwheel at a desired speed by adjusting the water pressure and the height of the gate.
Similarly, in an electrical circuit, the desired amount of work is allocated to various devices by changing the value of the resistance or voltage.

Ohm’s Law

The following relationship exists between current, voltage, and resistance:
Increasing voltage increases the amount of current.
Decreasing resistance increases the amount of current.
This relationship can be summarized as follows: the amount of current increases in direct proportion to the amount of voltage, and decreases in inverse proportion to the amount of resistance.
This relationship between voltage, current, and resistance is defined by Ohm’s law, which is represented by the following formula:
E = R x I
E: Voltage(V)
R: Resistance(Ω)
I: Current(A)

Electric Power
Electric power is represented by the amount of work performed by an electrical device in one second.
It is measured in watts (W), and 1W is the amount of power that is obtained when a voltage of 1 V is applied to a load resistance of 1Ω, and a current of 1 A flows for one second.

The amount of power is calculated with the following formula:
P = I x V
P: Amount of power, unit: W
I: Current, unit: A
V: Voltage, unit: V
If 5A of current is applied in one second using a voltage of 12 V, the electrical device performs 60W of work. (5 x 12 = 60)
Direct Current and Alternating Current
A current of constant direction with a magnitude that does not vary is called direct current. On the other hand, a current that reverses direction and has a variable magnitude is called alternating current.
1. Direct Current (DC)
This is a type of current that flows in a constant direction, from the positive pole to the negative pole, as in an automotive battery or a dry cell.
2. Alternating Current (AC)
This is a type of current that reverses direction at regular intervals. The electricity in the household outlets or industrial three-phase power supply used in factories is some examples.


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