In the International System of Units (SI), which unit is used to measure electric current, defined as the rate of flow of electric charge?

Introduction / Context:
Electric current is one of the seven base quantities in the International System of Units. It is central to the study of electricity and electronics, describing how much electric charge passes through a cross section of a conductor per unit time. The question asks you to identify the correct SI unit used to measure this base quantity from among several units that represent other physical concepts.

Given Data / Assumptions:
- Electric current is defined as charge flowing per unit time.- We use SI units throughout.- The options include units for force, energy, electric current, and power.

Concept / Approach:
In the SI system, the base unit of electric current is the ampere, symbol A. One ampere corresponds to one coulomb of charge passing through a cross section in one second. Newton is the unit of force, joule is the unit of energy, and watt is the unit of power. None of these match the definition of current as charge per unit time, making ampere the only correct choice.

Step-by-Step Solution:
1. Recall the relation I = Q / t, where I is current, Q is charge in coulomb, and t is time in second.2. From this, the unit of current is coulomb per second.3. In SI, coulomb per second is given the special name ampere, abbreviated as A.4. Examine the options: newton measures force, joule measures energy or work, watt measures power, and ampere measures current.5. Therefore, the correct SI unit of electric current is ampere.

Verification / Alternative check:
Everyday electrical ratings confirm this: household circuit breakers are rated in ampere, such as 6 A or 16 A, and fuses are specified similarly. Electrical instruments like ammeters are named after this unit. Also, in Ohm law, the relation V = I * R uses volt, ampere, and ohm as standard units of voltage, current, and resistance. These consistent uses verify that ampere is indeed the base unit for electric current in SI.

Why Other Options Are Wrong:
- Newton: Unit of force, equal to kilogram metre per second squared.- Joule: Unit of energy or work, equal to newton metre.- Watt: Unit of power, equal to joule per second.

Common Pitfalls:
Since all of these units appear frequently in physics, it is easy to mix them up under exam stress. A useful memory device is that ampere sounds like amp, a term widely used for current ratings in household and industrial contexts. Associating newton with forces, joule with energy, and watt with power will help keep these units clearly separated in your mind.

Final Answer:
The SI unit of electric current is the ampere.