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GATE 2020 AE – Question 14

Aerodynamics · Viscous flows: Hagen-Poiseuille flow, Couette flow and boundary layers · 1 mark · Multiple choice

At room temperature, increasing temperature has which effect on dynamic viscosity of water and air?

  1. Increases both.
  2. Increases water, decreases air.
  3. Decreases water, increases air.
  4. Decreases both.

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Show answer and explanation

Correct answer: (C) Decreases water, increases air.

Explanation

In liquid water, increased thermal agitation weakens the effective resistance associated with intermolecular cohesion, so viscosity decreases. In a gas such as air, increased molecular momentum transport raises viscosity with temperature. Thus C gives the correct opposite trends near room temperature.

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