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Electric Current

In an electric circuit, electric charges (electrons) can move through conductors.

This organized movement of charges constitutes electric current.

Current measures how much charge passes through a point in the circuit every second.

It can be compared to a water flow in a pipe:

  • if a lot of water flows through every second → the flow rate is high;
  • if very little water flows through → the flow rate is low.

Similarly:

  • if many charges pass through the conductor per second → the current is strong;
  • if few charges pass through → the current is weak.

Symbol and Unit

Current is generally denoted by \(I\).

Its unit in the International System is the ampere, denoted by \(\mathrm{A}\).

  • \(1\ \mathrm{A}\) means that a certain amount of charge passes through the conductor every second.

  • Smaller currents are often expressed in milliamps \((\mathrm{mA})\):

    • \(1\ \mathrm{mA} = 0{,}001\ \mathrm{A}\)

Examples of current values:

  • a few \(\mathrm{mA}\) for an LED or a small electronic sensor;
  • \(0.5\ \mathrm{A}\) to \(2\ \mathrm{A}\) for a phone charger;
  • \(5\ \mathrm{A}\) to \(10\ \mathrm{A}\) for a household appliance;
  • several tens of amperes for a powerful electric heater.

Direction of Current

In metals, it is the electrons that actually move.

They move from a negatively charged point to a positively charged point.

By convention, however, we define the direction of current as flowing from the positive terminal to the negative terminal.

This convention is used in all electrical diagrams and calculations, even though the actual movement of electrons is in the opposite direction.

Key Points: Electric Current

  • Current is the flow of charge through a conductor.
  • It is denoted by \(I\) and expressed in amperes \((\mathrm{A})\).
  • \(1\ \mathrm{A}\) = "high" current for small circuits; milliamps \((\mathrm{mA})\) are often used for low currents.
  • You can think of it as a water flow: the more charges passing per second, the higher the current.
  • By convention, the direction of current flows from + to −, even though electrons move in the opposite direction.

Order of magnitude

Select a type of device to see the typical order of magnitude of the current flowing through it.

- W
- V
- A

This estimate shows that, for a given voltage, the higher the power of a device, the greater the current flowing through it.