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⚛️ Physics  ·  Units and Measurements  ·  NEET & JEE

The Reynolds number Re, used to predict whether fluid flow is laminar or turbulent, is a dimensionless combination of fluid density ρ, velocity v, characteristic length L, and viscosity η. Which combination is dimensionally consistent with Re?

Answer: ρvL/η.

  • A ρv²L/η
  • B ρvL²/η
  • C ρv/(Lη)
  • D ρvL/η

Correct answer: D. ρvL/η

Explanation: Checking dimensions, [ρ][v][L]/[η] = [ML⁻³][LT⁻¹][L]/[ML⁻¹T⁻¹] is dimensionless, confirming Re = ρvL/η is the correct dimensionless group.

The 7 SI Base UnitsLengthmetre (m)fundamentalMasskilogram (kg)Timesecond (s)Electric Currentampere (A)Temperaturekelvin (K)Amount ofSubstancemole (mol)LuminousIntensitycandela (cd)Every other physical quantity is derived by combining powers of these 7 base units

The 7 SI base units. All derived units (newton, joule, watt, volt, etc.) can be expressed as combinations of these 7 fundamental units raised to various powers.

Concept context

SI base units, dimensional analysis, significant figures, and error propagation. The toolkit every physics calculation relies on.

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