Reference On Electricity, Part 3 | From - Expert Contractors

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Resistance

In a hydraulic system, the flow of fluid is impeded or resisted by friction between the wall of the pipe, fittings and other turns and offsets. In the same manner, the flow of current in a circuit (electrical wiring installation) is also impeded or resisted by the wire, transformer and other devices. This is called Impedance, the electrical term for Friction in AC electricity. In a direct current DC circuit, this Impedance is called Resistance. However, both are expressed in the unit of measure called Ohms.

Just as in a hydraulic scheme, the quantity of water flowing is proportional with the load and inversely proportional with the friction. Similarly, in thrilling path, the stream is proportional with the voltage and inversely proportional with the route resistance or load.


Thus:

1. The Higher the Voltage, the Larger the Current
2. The Higher the Resistance, the Lower the Current.

Their relationship may be expressed by the following equation know as the Ohms Law.

I = V/R

Where:

I = current
V = voltage
R = resistance for DC electricity

For AC electricity, the Ohms Law is expressed as :

I = V/Z

Where:

I = current
V = voltage
Z = impedance

The unit of current is the ampere (amp. or a.)

1.4 Comparison of AC and DC Electricity

Under the principles of DC electricity. Power is the product of voltage and Current.

Watts = Volts x Amperes

Under the principle of AC electricity, the product of volts and amperes is equal tot he quantity called volt-ampere (v.a.) which is not the same as watt. Thus:

Volt Amperes = Volts x Amperes

And to convert volt-amperes to watts or power, a power factor (pf) is introduced. And to get power in an AC circuit, we have the following formula:

Watts = Vots x Amperes x power factor

W = V x I x pf

1.5 The Ohms Law

In 1926, George Simon Ohm, a German scientist, discovered the relationship between the Current, Voltage and Resistance now referred to as the Ohms Law which states that:

"The higher the voltage, the larger the current, and the higher the resistance the lower the current."

The relationship between the current, voltage and resistance is presented in the following equations know as the Ohms Law.

I = V/R

Where:
I = Current flow (amperes)
V = Electromotive force (volts)
R = Resistance (Ohms)

1.6 Series and Parallel Circuit

A circuit components can be arranged in several ways but with two fundamentals types of connections, namely:

1. Series Circuit
2. Parallel Circuit

In Series Connection, a single path exist for current flow that is, the elements are arranged in a series one after the other with no branches. Being a single path in a series arrangement, voltage and resistance simply adds, thus:

Voltage total V1 = V1 + V2 + V3........

Resistance R1 = R1 +R2 +R3.........

In parallel circuit it sometimes referred to a as multiple connections where the loads are placed across the same voltage constituting a separate circuit. In hydraulic analogy, the connections are similar to branching pipe arrangement. Parallel Circuit is the standard arrangement for house wiring connection wherein the lights constitute one parallel grouping and the convenience wall outlets constitute the second parallel grouping.

The fundamental notion under this form of circuitry is that: " lots in parallel are additive for present and that each has the same voltage forced."

Examining further the Ohms Law as previously discussed. current is inversely proportional to the resistance. As resistance increases, current decreases. When current rises instantly to a very high level, the conditions will constitute a short circuit. Hence, it is mandatory for all circuit to be protected by fuse or circuit breaker that automatically open and disable the line in case of a fault or short circuit.