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General SciencePhysics: Units and Measurements

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Which of the following is a fundamental base unit in the SI system?

Joule

Ampere

Watt

Volt

Correct Answer

⚙️ TE • Technical Concept & PrincipleGeneral SciencePhysics: Units and Measurements

Option B

Ampere

Quick Summary:

The International System of Units (SI) defines seven base units that form the foundation for all other derived units. Among the given options, the Ampere is the base unit for electric current, while Joule, Watt, and Volt are derived units.

🔬SCScience SolutionConcept & Principle

💡 Explanation

💡 Everyday Analogy (Real-World Intuition)

Think of the Ampere as the 'flow' of water through a pipe; it measures the quantity of charge moving past a specific point in one second, much like liters per second define the flow rate of a river.

🧠 Memory Mnemonic / Shortcut Aid

Mnemonic for the 7 SI base units (M-L-T-A-K-M-L): 'Many Little Things Are Kept Mostly Locked' (Meter, Kilogram, Second, Ampere, Kelvin, Mole, Lumens/Candela).

🔢 Key Formulas

$I = \frac{dQ}{dt}$ — Ampere ( $A$ ) as the rate of flow of charge ( $Q$ ) per unit time ( $t$ )

$1 \text{ A} = 1 \text{ C/s}$ — The relation between Ampere, Coulomb, and Second

⚙️ Working Principle

The Ampere is defined by fixing the numerical value of the elementary charge $e$ to be $1.602176634 \times 10^{-19}$ when expressed in the unit $C$ (Coulomb), which is equal to $A \cdot s$ . It represents the constant current that, if maintained in two straight parallel conductors of infinite length and negligible circular cross-section, would produce a force equal to $2 \times 10^{-7} \text{ Newtons}$ per meter of length.

📌 Key Points

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There are exactly seven SI base units: meter ( $m$ ), kilogram ( $kg$ ), second ( $s$ ), ampere ( $A$ ), kelvin ( $K$ ), mole ( $mol$ ), and candela ( $cd$ ).
▸
Derived units are expressed as products or quotients of these seven base units.
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Joule ( $J = kg \cdot m^2 \cdot s^{-2}$ ), Watt ( $W = J/s$ ), and Volt ( $V = W/A$ ) are all derived from base units.

✅ Advantages

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Provides a coherent and universal system for scientific measurement worldwide.
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Ensures consistency in experimental data across different scientific disciplines.

🛠️ Applications / Uses

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Electrical circuit design and power distribution systems.
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Standardization in international trade and scientific research.

📄 Additional Information

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The Ampere is the only SI base unit that defines an electromagnetic property directly.
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Option A (Joule) is the derived unit of energy. Option C (Watt) is the derived unit of power. Option D (Volt) is the derived unit of electric potential difference.

📊 Diagram / Illustration

✅

B is correct — Ampere is one of the seven fundamental base units defined in the SI system.

Core Concepts Used

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SI Base Units Dimensional Analysis Electric Current

💡 EXAM TIP

Always distinguish between base units and derived units; if a unit can be broken down into combinations of $kg$ , $m$ , $s$ , $A$ , $K$ , $mol$ , or $cd$ , it is a derived unit.

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