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In every closed electrical circuit, current performs work, and the amount of work depends on the strength of the current. The greater the current, the more work it does. However, there is another quantity that affects the work, and it is called electric voltage or simply voltage.

Voltage is a physical quantity that numerically equals the work done by an electric field in moving a unit positive charge along a certain path.

Voltage is denoted by the letter U.


A – the work done by the electric field during the flow of current;

q – the value of the electric charge carried by the current.

To understand this concept, let’s conduct an experiment.

In the diagram, there are two electrical circuits: one with a lamp powered by a pocket flashlight where the power source is a battery, and the other with a regular light bulb powered by the city’s electrical network.

Looking at the ammeter readings, the strength of the current in both electrical circuits is the same. However, the bulb connected to the city’s electrical network gives more light than the one connected to the pocket flashlight. This is because the electric voltage across the bulbs is different at different currents.

The bulb from the pocket flashlight lights up with low voltage when each coulomb of electricity passes through its spiral, performing a small amount of work, thus giving less light. The second bulb lights up with much higher voltage. When each coulomb of electricity passes through its spiral, it performs more work, resulting in more light.


The electric voltage at the ends of a section of the circuit is numerically equal to the work done when one coulomb of electricity passes through that section. The greater the work, the higher the voltage at the ends of the circuit.

Measurement of voltage

Voltage is denoted by the letter U. The unit of voltage is the volt (V), named after the Italian scientist Alessandro Volta, who created the first galvanic element.

1 volt is the voltage at which the work done along a section of the circuit is equal to 1 joule when 1 coulomb of electricity or one electric charge passes through this section.

To measure voltage, voltmeters are used.

Voltmeter notation in electrical circuits:

Voltmeters are always connected in parallel. The voltmeter’s terminals are connected to the points in the circuit between which the voltage needs to be measured. A voltmeter in an electrical circuit is always connected in parallel.

Alternatively, voltage can be calculated using Ohm’s law by measuring the current strength and resistance or using combined devices such as a multimeter.