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JEE Main 2025 Jan 28 Shift 1, Physics Q3: Properties of Fluids

JEE Main2025Jan 28, Shift 1Physics
Q.

Consider following statements:

A. Surface tension arises due to extra energy of the molecules at the interior as compared to the molecules at the surface, of a liquid.
B. As the temperature of liquid rises, the coefficient of viscosity increases.
C. As the temperature of gas increases, the coefficient of viscosity increases.
D. The onset of turbulence is determined by Reynold's number.
E. In a steady flow two stream lines never intersect.

Choose the correct answer from the options given below :

  1. A

    A, D, E only

  2. B

    C, D, E only

  3. C

    B, C, D only

  4. D

    A, B, C only

Solution

A. Surface tension comes from surface molecules having higher energy than interior molecules (fewer neighbours to bond with). The statement reverses this. False.

B. Liquid viscosity arises from intermolecular cohesion; rising temperature weakens cohesion and the viscosity decreases. False.

C. Gas viscosity arises from molecular momentum transport. Higher temperature increases molecular speeds and thus increases. True.

D. Reynolds number determines whether flow becomes turbulent. True.

E. In steady flow, the velocity at each point is fixed in time; two intersecting streamlines would assign two velocities to one point, which is impossible. True.

C, D, E only.

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