Electric current

What Is an Amp (ampere)?

The ampere (symbol: A) is the SI base unit used to measure the intensity of the electric current.

What is an amp (ampere)?

It takes its name from the French physicist André-Marie Ampère (1775-1836), one of the leading scholars of electromagnetism.

Being one of the seven basic SI units, all other electromagnetic units are derived from it. By definition, an ampere is the intensity of an electric current that, if maintained in two parallel linear conductors of infinite length and insignificant cross section, placed one meter apart from each other in a vacuum, produces a force equal to each other to 2 × 10 -7 N for each meter in length. 

The correct way to write ampere is with the initial lowercase letter, except when according to the grammatical rules you must write a word with the initial use of capital letters.

The ampere is of importance, therefore, in the field of electricity. This unit appears in the calculation of the dimensioning of a photovoltaic solar energy installation.

A device called an ammeter is used to measure current intensity.

What Is the Definition of Ampere?

There are two definitions of amp:

  • Definition of ampere based on electrical phenomena.
  • Definition of ampere based on magnetic phenomena.

Definition of Ampere Based on Electrical Phenomena

The ampere expresses the intensity of the current in a conductor crossed in any section since the charge of a coulomb in the time of one second.

By analogy, the intensity of the current is comparable to the amount of water that passes through a tube measured in kg / second, where the mass of water represents the electric charge.

The electric charge, that is, the amount of electrons, can be expressed in ampere-hours (Ah). The ampere-hour is the total amount of charge that flows, with the intensity of one amperage, into a conductor in one hour.

With such a size, for example, the maximum charge accumulated by the batteries is measured: the car battery contains approximately 55 Ah.

Within SI units, equality applies:


With "C" for coulomb, "s" for second, "V" for volts, "Ω" for ohms and "W" for watts. The absence of coefficients is due to the fact that the International System is a coherent measurement system, which means that the product or the quotient of several units gives rise to a new unit of unit value.

Definition of Ampere Based on Magnetic Phenomena

According to Ampere's law, the ampere can be defined as the current intensity that must flow in two cables of infinite length and is placed at a distance of one meter, so that they attract with a force equal to 2 × 10 - 7   N / m.

Measurement Samples

Due to the difficulty in measuring the forces between two conductors, the so-called international ampere or statampere was proposed: defined in terms of silver deposition rate (the international ampere is the intensity of a current that, through a solution of AgNO 3 [monovalent Ag], deposited on the cathode 0.001118 g of silver in one second), is equal to 0.99985 A.

This unit of measurement, however, is considered obsolete.

Currently, however, most national metrological institutes use sample stacks and resistors for the maintenance of primary amperage samples.

The sample of electric current intensity is derived from Ohm's law using two samples, one of emf and one of resistance.

The emf sample is a group of saturated Weston heaps, controlled by the Josephson effect; electrical resistance is defined as the average resistance of a group of 10 sample resistors in 1 Ω manganin.

In order to avoid the influence of the contact resistance between the resistance and the measurement circuit, the sample resistors exhibit a particular four terminal embodiment: two external amperometric through which the resistance is subject to the passage of electric current, and two of internal voltage compared to amperometrics, from which the voltage drop caused by the circulation of the electric current is eliminated.

What Is the Difference Between Volt and Ampere?

The volt is the unit of the international system of measurements for measuring the voltage of an electric current. Ampere is the unit of international measurement system for measuring current intensity.

Therefore, we should know:

What Is the Difference Between Voltage and Current Intensity?

The intensity of an electric current is the electric charge (number of electrons) that circulates in a conductor per unit time (per second). On the other hand, the voltage of an electric current is the force with which it does it. This difference is called the potential difference.


Making the comparison with a water pipe we can imagine that the electrons are drops of water. In this case, the current intensity is the quantity of drops of water that circulates through the pipe. In this simile, pressure is the difference in potential or current voltage. 


Published: September 6, 2018
Last review: April 10, 2020