Question

What is the effect of temperature increase on viscosity of liquids and gases?

(a) Increases for both liquids and gases

(b) Increases for liquids and decreases for gases

(c) Increases for gases and decreases for liquids

(d) Decreases for both liquids and gases

This question was addressed to me in semester exam.

My doubt is from Fluids Mechanical Properties topic in chapter Mechanical Properties of Fluids of Physics – Class 11

Answer 1

Right choice is (c) Increases for gases and decreases for liquids

To explain I would say: In the case of liquids when temperature increases, viscosity decreases because it is the result of molecular bonds (electromagnetic forces) between particles which weaken due to random motion brought about by increase in temperature.                                                                                                 In the case of gases, the molecules vibrate more randomly, leading to more obstruction in the path of bodies trying to move through it. And we interpret this increased obstruction as increased viscosity of the gas.