Which of the following expressions correctly defines one ampere?

The correct option is 1 coulomb per second.

Explanation

Electric current is defined as the rate of flow of electric charge through a cross-section of a conductor. The SI unit of current is the Ampere (A), and the SI unit of charge is the Coulomb (C).

Analysis of Options:

• 1 coulomb per second Correct: Mathematically, current ($I$) is expressed as the ratio of charge ($Q$) to time ($t$), i.e., $I = Q/t$. Therefore, 1 Ampere is defined as the flow of 1 Coulomb of charge per second ($1 \text{ A} = 1 \text{ C/s}$).
• 1 joule per coulomb Incorrect: 1 Joule per Coulomb represents the unit of electric potential or electromotive force, known as the Volt ($V = W/Q$).
• 1 volt per ohm Incorrect: 1 Volt per Ohm equals 1 Ampere according to Ohm’s Law ($I = V/R$). However, this is a behavioral relationship for ohmic conductors rather than the fundamental definition of the unit of current.
• 1 watt per volt Incorrect: 1 Watt per Volt equals 1 Ampere based on the power formula ($P = VI$), but this is a derived relationship, not the definition.

Key Takeaway:
The Ampere is the SI unit of electric current, fundamentally defined as the transfer of one Coulomb of charge per second.