VOLT OR VOLT: CONCEPT AND FORMULAS, EQUIVALENCES, EXAMPLES - PHYSICAL - 2025

The volt or volt is the unit used in the International System of SI Units to express voltage and electric potential, one of the main magnitudes of electricity. Voltage does the work necessary to start electrical charges and thereby create a current. Electric current, traveling through conductors, is capable of starting motors, transmitting information, lighting avenues and homes, and much more.

The name volt as a unit, was chosen in honor of Alessandro Volta (1745-1827), the Italian physicist and chemist who invented the electric battery around 1800. At that time, the anatomist Luigi Galvani had verified that frog legs could be contract by applying electricity. Volta, aware of these results, also set about looking for electrical charges in animal tissues, using an electroscope.

Figure 1. Assortment of AA batteries with a nominal voltage of 1.5 V, widely used in small devices, such as radios, cameras, flashlights and toys. Source: Pixabay.

However, Volta did not find what he was looking for in organic materials and was finally convinced that the electrical charges were, somehow, in the metals with which he touched the frog legs.

Figure 2. Portrait of Alessandro Volta. Source: Wikimedia Commons.

Volta also realized that two different metals produced a potential difference and that some combinations were better than others. This is how he built the first battery: sheets of felt moistened in saline solution between two silver and zinc electrodes. He piled up several of these layers and thus was able to produce a stable electrical current.

Concept and formulas

In 1874 the volt, along with the ohm, were adopted as units for voltage and resistance respectively, by a commission of the British Association for the Advancement of Science (BAAS) made up of notable scientists from around the world.

At that time, they were called “practical units” and today they are part of the International System of Units or SI.

In most of the literature, the potential difference is defined as energy per unit charge. Indeed, if you have an electric charge in the middle of an electric field produced by another charge, you need to do work to make them move from one place to another.

The work done is stored in the configuration of charges as a change in their electric potential energy, which we will call ∆U. The symbol ∆ indicates this change or difference, since ∆U = _Final U - _{Initial Initial}.

In this way, the potential difference between two points ∆V is defined as:

Since energy has units of joule (J) and charge comes in coulomb (C), a voltage of 1 volt (V) equals 1 joule / coulomb:

Thus, 1 volt equates to a potential difference doing the work of 1 joule for each coulomb.

Alternative definition of volt

Another way to define the volt is by linking electrical current and power. In this way, 1 volt (V) is the potential difference between two points on a wire through which a current of 1 ampere (A) circulates if the power dissipated is 1 watt (W). Thus:

This definition is important because it involves the intensity of electric current, which is one of the fundamental magnitudes of physics. Therefore, the ampere belongs to the group of seven fundamental units:

It is possible to check that both definitions are equivalent, knowing that 1 watt is 1 joule / second and 1 ampere is 1 coulomb / second, hence:

The seconds are canceled, and J / C remains, equivalent to 1 newton. meter / coulomb. Therefore 1 volt is also expressed as:

Ohm's law

For some materials, a linear relationship between the voltage (V), the current (I) and the electrical resistance (R) of a material is fulfilled, which is known as Ohm's law. Thus:

Since the units for electrical resistance are ohms (Ω), it turns out that 1 V = 1 A.Ω

Equivalences

To measure voltages, the multimeter or tester and the oscilloscope are mainly used. The first offers a direct measurement of voltage and the second has a screen to display the shape of the signal, as well as its value.

Figure 3. Digital multimeter used to measure various electrical quantities. Source: Pixabay.

It is common to find values ​​much higher or lower than the volt, therefore it is useful to have the equivalences between the multiples and the submultiples:

-1 kilovolt (kV) = 1000 V

-1 millivolt (mV) = 10 ^-3 V

-1 microvolt (μV) = 10 ^-6 V

Examples

Voltages in biology

In the heart there is an area called the sinus node, which behaves like a battery by generating electrical impulses that stimulate the heartbeat.

The graph of the same is obtained by means of an electrocardiogram, which offers the values ​​of the cardiac cycle: duration and amplitude. Thanks to this, abnormalities in the functioning of the heart can be detected.

Typical values ​​of the membrane potential, inside the heart, are between 70-90 mV, while the electrocardiograph is capable of recording voltages of the order of 1 mV.

Figure 4. An electrocardiogram records the electrical activity of the heart. Source: Pixabay.

The nervous system also works by electrical impulses. Voltages of about 70 mV can be measured in the nerves of humans.

Voltages on Earth

The Earth has its own electric field directed towards the interior of the planet, in this way it is known that it is negatively charged. Between the surface and the upper layers of the atmosphere there are fields whose magnitude varies between 66-150 N / C, and potential differences of up to 100 kV can be established.

On the other hand, the natural currents that flow in the subsoil, allow to characterize a terrain through the use of electrical methods in geophysics. A test consists of inserting electrodes in the field, two for voltage and two for current and measuring the respective magnitudes.

By varying the configuration of the electrodes in different ways, it is possible to determine the resistivity of the ground, a property that indicates how easy or difficult current can flow in a given material. Depending on the values ​​obtained, the existence of an electrical anomaly can be inferred, which may indicate the existence of certain minerals in the subsoil.

Voltages in commonly used devices

-Home power network (alternating voltage): 110 V in America and 220 in Europe.

-Spark plugs in the car: 15 kV

-Car battery: 12V

-A dry battery for toys and flashlights: 1.5 V

-Voltage in a smartphone battery: 3.7 V.

References

1. International Electrotechnical Commission IEC. Historical Background. Recovered from: iec.ch.
2. Griem-Kee, S. 2016. Electrical methods. Recovered from: geovirtual2.cl.
3. Kirkpatrick, L. 2007. Physics: A Look at the World. 6 ^ta Editing abbreviated. Cengage Learning.
4. Knight, R. 2017. Physics for Scientists and Engineering: a Strategy Approach.
5. The Physics Factbook. Electric Field on Earth. Recovered from: hypertextbook.com.
6. Wikipedia. Electrocardiogram. Recovered from: es.wikipedia.org.
7. Wikipedia. Physical magnitude. Recovered from: es.wikipedia.org.