Physical Quantities And Units

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Among the following commonly used units in physics, which one is a fundamental SI base unit rather than a derived unit?

RankGuru · Accepted Answer

The International System of Units recognises seven fundamental base quantities, each having an independently defined unit that is not constructed from any other units. The mole is the SI base unit for the amount of substance, fixed through the defined value of the Avogadro constant, and therefore qualifies as a genuine fundamental unit. The newton is the unit of force and is derived, since Newton's second law gives it as kg·m·s^-2. The pascal measures pressure and is derived as N·m^-2, which expands to kg·m^-1·s^-2 in base units. The joule is the unit of energy and reduces to kg·m^2·s^-2, again a product of base units. Distinguishing primary from derived units is foundational for dimensional analysis, because only the seven base dimensions generate every derived dimension used throughout NCERT physics. A quick verification confirms the answer: only the mole cannot be expressed using metre, kilogram and second, so among the four options it alone is a true base unit.

Physical Quantities And Units

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