Q136 / 160 · AP EAMCET 2022 (04 Jul Shift 1) · Physics

Statement (A): When the temperature increases the viscosity of gases increases and the viscosity of liquids decreases.

Statement (B): Water does not wet an oily glass because cohesive force of oil is less than that of water.

Statement (C) : A liquid will wet a surface of a solid if the angle of contact is greater than 90°.

  • A
    A. B. and C are false
  • B
    A and B false,
    C is true
  • Correct answer
    C
    B and C false, A is true
  • D
    A and C false, B is true

Solution

Statement A:

In liquid: With the rise in temperature, viscosity of a liquid decreases because the intermolecular attractive force between consecutive layers decreases as temperature increases. 

In gasses: The important cause of viscosity is randomness/molecular collision due to root mean square velocity. Due to rise in temperature, kinetic energy of molecules increases which makes rms velocity increase, hence randomness and collision of molecules increases. This makes the flow difficult and hence viscosity in gasses increases with temperature.

Statement B:

Water does not wet an oily glass, because  cohesive force for water > adhesive force between water and oil molecules.

Statement C:

When the liquid does not wet the sides of a solid object, it means that the angle of contact is more than 90° but less than 180°.

Hence, the correct answer is option: 'C'.

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