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Revision as of 18:09, 25 February 2022

This page explains the difference between series and parallel circuits, why it matters, and the implications.

Summary

You have maybe heard of series and parallel circuits but not known what they are, or whether you even need to know. There are important differences in the way the voltage and current are distributed, which are helpful to understand.

Safety

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Series circuits

A series circuit is one where the current is forced to flow through one component after another, arranged in a line.

Often, for example, a number of LEDs will be connected in series. If a certain voltage (or electrical pressure) is needed to drive the required current though one LED, then it will take twice the voltage to drive it through two in series, or n times the voltage to drive it through n LEDs.

Older Christmas tree lights usually consisted of many low voltage filament bulbs in series. So a set of 80 lights might consist of 80 bulbs rated at 3V each, 80 x 3V being 240V, the standard mains voltage.

The relationship between the current through a LED or a filament bulb and the voltage isn't simple, and so let's think about resistors. In these, twice the voltage produces exactly twice the current. So if you connect two resistors in series across a battery, the total battery voltage will be divided between the two according to their resistances.

For example, if you connect a 100Ω and a 200Ω resistor in series to a 3V battery and measure the voltage across each resistor, you will find 2V across the 200Ω resistor, and 1V across the 100Ω resistor, totalling 3V.

Such an arrangement is therefor sometimes called a voltage divider. Tis is how the volume control in an older radio works. The audio signal is presented across the ends of a carbon track, having a certain resistance, in the volume control. As you turn up the volume from zero, a contact moves progressively from the bottom of the track, where there is no voltage, to the top, where the voltage is the full voltage of the audio signal. A third of the way up, it will tap off a third of the signal, and so on.

Parallel circuits

External links

External links (if any) as bullet points.
If none, delete this section.

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 ::Consider whether your page should include a specific section on safety.
-==The water analogy==
+==Series circuits==
-The flow of water is often a useful (though not perfect) analogy for the flow of electricity, as shown (humourously) in this [https://xkcd.com/2571/ xkcd cartoon].
+A series circuit is one where the current is forced to flow through one component after another, arranged in a line.
-Water pressure is rather like voltage, which is in fact the electrical "pressure" driving a current around a circuit against certain resistance.
+Often, for example, a number of LEDs will be connected in series. If a certain voltage (or electrical pressure) is needed to drive the required current though one LED, then it will take twice the voltage to drive it through two in series, or n times the voltage to drive it through n LEDs.
-Water flow (in litres/minute, or whatever you like) is analogous to the electrical current in Amps. A current of 1 Amp flowing around a circuit corresponds to 6.25 billion billion electrons per second passing any given point.
+Older Christmas tree lights usually consisted of many low voltage filament bulbs in series. So a set of 80 lights might consist of 80 bulbs rated at 3V each, 80 x 3V being 240V, the standard mains voltage.
-If a water pipe contains a constriction, there will be a greater pressure drop across the constriction than over the unconstricted length free flowing length. In the same way, there is a voltage (electrical pressure) drop across any resistance in a circuit, the greatest voltage drop across the greatest points of resistance.
+The relationship between the current through a LED or a filament bulb and the voltage isn't simple, and so let's think about resistors. In these, twice the voltage produces exactly twice the current. So if you connect two resistors in series across a battery, the total battery voltage will be divided between the two according to their resistances.
-If a river can flow through several alternate channels, the flow will distribute itself according to the width of the channels, with most flowing through the widest. In the same way, if electricity is given several paths it can follow, the most current will flow through the path offering the least resistance.
+For example, if you connect a 100Ω and a 200Ω resistor in series to a 3V battery and measure the voltage across each resistor, you will find 2V across the 200Ω resistor, and 1V across the 100Ω resistor, totalling 3V.
-Unlike water, electricity can't just spill out, but can only flow if it can flow all the way around a circuit, perhaps through many different paths on the way.
+Such an arrangement is therefor sometimes called a voltage divider. Tis is how the volume control in an older radio works. The audio signal is presented across the ends of a carbon track, having a certain resistance, in the volume control. As you turn up the volume from zero, a contact moves progressively from the bottom of the track, where there is no voltage, to the top, where the voltage is the full voltage of the audio signal. A third of the way up, it will tap off a third of the signal, and so on.
+==Parallel circuits==
 ==External links==