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Electronics 101: Current

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What is current?

Current is defined as the flow of charged particles around a circuit. We call this electricity.

These charged particles are called electrons. The most important thing to remember about electrons is that they are negatively charged.

The Physics

Take a look at the diagram below. Imagine this is a copper wire connected to the positive and negative terminal of a battery.

When a circuit is complete, electrons move toward the positive terminal. This is due to their negative charge. They are attracted toward the positive terminal and are repelled away from the negative terminal.

Copper wire is used used to transport electricity because it is a very good conductor. Copper contains many free electrons, so it is perfect for this. The movement of these free electrons causes a transfer of energy throughout the circuit, this is what we define as current flow.

Does current "Flow" around a circuit?

Lets take an example of a simple battery-light bulb circuit. During a discharge of electricity, chemical reactions occur in the electrodes of the battery. This causes the anode to release electrons to the negative terminal.

The negative terminal of the battery can only physically hold a limited number of electrons. Eventually, there is nowhere else for the electrons to go, so they are pushed away from the negative terminal. This causes electrons to collide with one-another, resulting in an energy transfer around the entire circuit. This is how current "flows".

Don’t think of current as a flow of electrons. Think of it more as a flow of energy.

So which way does current Flow?

Based on what we have just learned. We now know that electrons are negatively charged, and therefore flow from negative to positive. The diagram below illustrates this.

You may have also heard of conventional current flow. Conventional current flow is an assumption that positive charge carriers cause current to flow. This assumption was made by Benjamin Franklin in the 1700’s.

 

This would mean that current flows in the opposite direction to electrons (positive to negative). We now know this to be untrue. But it’s worth noting, since this assumption is still used today.

This can be a little confusing, but don’t be too bothered by it. Just remember that they are complete opposites.

How is current measured?

Current is measured in Coulombs per second (total charge passing through a cable per second). However, current is almost always referred to in Amps.

Typically, we measure current with an instrument called an ammeter. These days you can by a multi meter instead, which is essentially voltmeter and ammeter in one, They also do many other useful things.

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