Understanding the Ampere: The Base Unit for Electric Current

The question asks to identify the base unit, discovered in 1820, that represents one coulomb of electric current per second. This definition directly relates to the fundamental concept of electric current.

What is Electric Current?

Electric current is defined as the rate at which electric charge flows past a specific point or area. The SI unit for electric current is the Ampere (A).

Mathematically, electric current (\(I\)) is expressed as the amount of charge (\(Q\)) passing through a point per unit time (\(t\)):

\(I = \frac{Q}{t}\)

Here, \(Q\) is measured in Coulombs (C) and \(t\) is measured in seconds (s). Therefore, the unit of current, the Ampere (A), is equivalent to Coulombs per second (C/s).

\(1 \text{ Ampere} = \frac{1 \text{ Coulomb}}{1 \text{ Second}}\)

This matches the description given in the question: "one coulomb of electric current per second" (though phrased slightly unconventionally, it means one coulomb of charge per second).

Historical Context of the Ampere

The Ampere is named after the French physicist André-Marie Ampère. Ampère's foundational work on electromagnetism, establishing the relationship between electric currents and magnetic fields, occurred around the year 1820. While the formal definition and standardization of the Ampere as an international unit happened later, his discoveries in this period were crucial and led to the unit being named in his honor. The date 1820 strongly points towards Ampère and his work on electric current.

Analyzing the Options

Let's look at the other options to see why they are not the correct base unit in this context:

• Volt: The Volt (V) is the SI unit for electric potential difference or voltage. It is not a base unit but a derived unit (Joules per Coulomb, or Watts per Ampere). It represents energy per unit charge, not charge per unit time.
• Kelvin: The Kelvin (K) is the SI base unit for thermodynamic temperature. It is unrelated to electric current or charge flow.
• Candela: The Candela (cd) is the SI base unit for luminous intensity. It measures the power emitted by a light source in a particular direction, per unit solid angle. It is unrelated to electric current.
• Ampere: As discussed, the Ampere (A) is the SI base unit for electric current and is defined in terms of charge (Coulomb) and time (second). Its name and context are strongly linked to the work done around 1820.

Based on the definition provided ("one coulomb of electric current per second") and the historical context (discovered/related to work around 1820), the unit that fits is the Ampere.

Conclusion

The base unit that represents one coulomb of electric current per second is the Ampere, a definition consistent with the flow of electric charge over time. The historical reference to 1820 aligns with the period of André-Marie Ampère's significant contributions to the understanding of electricity.

Revision Table: Key SI Base Units

Additional Information: Defining the Ampere

The definition of the Ampere has evolved over time. Until May 20, 2019, the Ampere was defined based on the force between two parallel, current-carrying conductors. The current definition, part of the revised SI, is based on the fixed numerical value of the elementary charge, \(e\). The elementary charge is \(1.602\,176\,634 \times 10^{-19}\) Coulombs.

The Ampere is now defined such that the elementary charge \(e\) is equal to \(1.602\,176\,634 \times 10^{-19}\) C. Since 1 Coulomb is the charge of \(1 / (1.602\,176\,634 \times 10^{-19})\) elementary charges, and 1 Ampere is 1 Coulomb per second, this modern definition fundamentally links the Ampere to a specific number of elementary charges passing a point per second.

This new definition provides a more precise and stable basis for the unit, though the conceptual understanding of the Ampere as Coulombs per second remains valid and essential.