Current flows against voltage


Voltage U [volts]

But how does the electrical charge of a conductor get into motion? When charges are separated, a voltage builds up. The separated charges “want” to reunite. This is known as tension. Electric current flows due to voltage differences (potential differences)
between the poles of a voltage source.
The higher the voltage, the greater the electrical current in a circuit. (Water analogy: the greater the water pressure on a pipe, the more water flows through it).

Voltage is measured in volts (by Alessandro Volta). The symbol is U (from the Latin urgere = push, drive, press).

Voltage can be created in several ways:

  • Friction: Try with a plastic stick that we rub with a cloth.
  • Battery: chemical processes generate the voltage
  • Induction: Magnet moves around a coil (a conductor loop)

voltage can also be generated by heat (thermocouple), light (solar cells) or pressure (piezo element).

Resistance R [Ohm]

If current flows through a metallic conductor, the free electrons move between the atoms of the conductor. The atoms swing in all directions around their position of rest. This hampers the movement of the free electrons. Each conductor therefore opposes the electrical current with a resistance which the voltage has to overcome.

Resistances are measured in ohms (physicist Georg Simon Ohm).

Current I [amps]

It is the amount of electrical current that flows through a conductor in a given time. It is measured in amperes.