Learn refrigeration

Resistance is a force which opposes the flow of an electric current around a circuit.  Voltage is required to push the charged particles around the circuit to push through resistance. The circuit itself will resist the flow of particles especially if the wires are either very thin or very long.

There are three main factors that effect resitance in an electrical circuit.

1 - The type of material – Electrons find it easier to pass through some materials than others such as metal. 

2 – The length of the wire in a circuit – If the length of a wire is doubled, the resistance is also doubled. This is because twice the length of wire is equivalent to two equal resistances in series.

3 – Thickness of a wire – A thicker wire has a  larger cross section and more electrons. This enables more electric current pass through on a given voltage with less resistance..

When electrons move against the opposition of resistance, “friction” is generated. Just like mechanical friction, the friction produced by electrons flowing against a resistance generates heat energy.

A good example of friction at work is a lamp’s filament. The lamp has a very thin wire and the friction being created by electric current passing through it causes a large amount of heat energy being manifested at that filament.

This heat energy is enough to cause the filament to glow white-hot, producing light, whereas the wires connecting the lamp to the battery (which have much lower resistance) hardly even get warm while conducting the same amount of current.

A resistor is a component of an electrical circuit that is specially resists the flow of electrical current. A resistor has two terminals across which electricity must pass, and is designed to drop the voltage of the current as it flows from one terminal to the next.

A resistor is primarily used to create and maintain a known safe current within an electrical component.

Resistance and the Ohm

Resistance is measured in Ohms  (symbol: Ω) .

The bigger the resistance, the smaller the current.

An ohm (symbol: Ω) is a resistance in a conductor that produces a potential difference of one volt when a current of one amp is flowing through it.

To calculate the resistance of a component. Firstly, we need to measure the current flowing through it, and the voltage across the component.

If the ammeter reads 3 A, and the voltmeter reads 9 V across the component,.

  Resistance = Volts divided by current (amps).

    R = V / I
    R = 9 / 3
    R = 3 Ohms