The rate of flow of electric charge through a conductor is called electric current. This rate is measured in which SI unit?

Introduction / Context:
Electric current is one of the fundamental concepts in circuits and electronics. It describes how much electric charge passes through a cross section of a conductor in a given time. Knowing the correct SI unit for current is essential when interpreting circuit diagrams, using ammeters, or applying Ohm law. This question asks which unit is used to measure the rate of flow of electric charge.

Given Data / Assumptions:

• Electric current is defined as charge flowing per unit time.
• The symbol for current is I, for charge is Q, and for time is t.
• The options include ampere, coulomb, ampere per coulomb, and ampere coulomb.
• We assume standard SI definitions for electrical quantities.

Concept / Approach:
By definition, electric current I equals Q divided by t. In SI, the base unit for current is the ampere, which is one of the seven base units of the International System of Units. One ampere is defined as one coulomb of charge passing through a cross section in one second. Coulomb represents the quantity of charge, not the rate. Combinations like ampere per coulomb or ampere coulomb are not standard physical units of basic quantities and are not used for current.

Step-by-Step Solution:
Step 1: Write the definition of current: I = Q / t, where Q is charge and t is time. Step 2: Recognise that the SI base unit for current is called the ampere, symbol A. Step 3: Note that one ampere corresponds to the flow of one coulomb of charge per second, so 1 A = 1 C / s. Step 4: Understand that coulomb by itself measures total charge, not the rate at which it flows. Step 5: Therefore, the rate of flow of charge, that is electric current, is measured in amperes.

Verification / Alternative check:
All circuit diagrams and electrical instruments label current in amperes or multiples like milliampere. Ammeters are calibrated in amperes, while voltmeters measure voltage in volts and energy meters in kilowatt hour. These practical conventions align with the theoretical definition that the SI unit of current is ampere. No instrument measures current directly in coulombs or in combinations like ampere coulomb in common practice.

Why Other Options Are Wrong:
Coulomb: This is the unit of electric charge, representing the quantity of charge, not its flow per second. Ampere per coulomb: This combination does not have a standard physical meaning for basic electrical quantities and is not used for current. Ampere coulomb: This product would represent a mixed unit with no simple interpretation as a basic electrical quantity.

Common Pitfalls:
Students sometimes confuse coulomb and ampere because they both appear in formulas about current. A useful memory aid is that coulomb measures “how much charge” there is, whereas ampere tells you “how fast the charge is flowing” through a conductor. Always associate current with rate and ampere, and charge with amount and coulomb.

Final Answer:
The rate of flow of electric charge, or electric current, is measured in ampere in the SI system.