Which Of The Following Is Not A Fundamental Unit

Which of the Following is NOT a Fundamental Unit? Understanding SI Units and Derived Units

This article will explore the concept of fundamental units within the International System of Units (SI), clarifying the difference between fundamental and derived units and providing examples. Understanding this distinction is crucial for accurate scientific measurement and reporting. We'll examine various units and determine which ones are not considered fundamental.

The International System of Units, or SI, is the modern form of the metric system. It's based on seven fundamental units, forming the foundation upon which all other units are built. These fundamental units are independent of each other, meaning none can be expressed as a combination of the others. Any unit that can be expressed as a combination of these fundamental units is considered a derived unit.

The Seven Fundamental SI Units

Let's review the seven fundamental units that define the SI system:

1. Meter (m): The unit of length. It represents the distance traveled by light in a vacuum during a specific time interval.
2. Kilogram (kg): The unit of mass. It's defined based on a specific platinum-iridium cylinder kept at the International Bureau of Weights and Measures.
3. Second (s): The unit of time. Defined based on the transitions of the cesium-133 atom.
4. Ampere (A): The unit of electric current. It's defined based on the force between two parallel conductors.
5. Kelvin (K): The unit of thermodynamic temperature. It's a scale based on absolute zero.
6. Mole (mol): The unit of amount of substance. It represents a specific number of elementary entities (atoms, molecules, ions, etc.).
7. Candela (cd): The unit of luminous intensity. It measures the power emitted by a light source in a specific direction.

Derived Units: Combinations of Fundamentals

Derived units are formed by combining the fundamental units using mathematical operations like multiplication and division. For example:

• Velocity (m/s): Derived from length (meter) and time (second).
• Force (kg⋅m/s² or Newton, N): Derived from mass, length, and time.
• Energy (kg⋅m²/s² or Joule, J): Derived from mass, length, and time.
• Pressure (kg⋅m⁻¹⋅s⁻² or Pascal, Pa): Derived from mass, length, and time.
• Electric Charge (A⋅s or Coulomb, C): Derived from electric current and time.

Identifying Non-Fundamental Units

Now, let's consider some examples to illustrate which units are not fundamental. If a unit can be expressed using a combination of the seven fundamental units listed above, it's a derived unit, and therefore, not fundamental. For example:

• Newton (N): A unit of force, it's a derived unit (kg⋅m/s²).
• Joule (J): A unit of energy, it's a derived unit (kg⋅m²/s²).
• Pascal (Pa): A unit of pressure, it's a derived unit (kg⋅m⁻¹⋅s⁻²).
• Watt (W): A unit of power, it's a derived unit (kg⋅m²/s³).
• Volt (V): A unit of electric potential, it's a derived unit (kg⋅m²⋅s⁻³⋅A⁻¹).

Therefore, any unit that is not listed among the seven fundamental units of the SI system—meter, kilogram, second, ampere, kelvin, mole, and candela—is a derived unit and is not a fundamental unit. Understanding this fundamental distinction is essential for accurate scientific calculations and communication.