Question

As temperature increases:

• A. The dynamic viscosity of a gas increases.
• B. The dynamic viscosity of a liquid decreases.
• C. The dynamic viscosity of a liquid does not change.
• D. The dynamic viscosity of a gas decreases.

Hint:

For gases, dynamic viscosity increases with temperature, while for liquids, it typically decreases with temperature.

Answer 1

The Correct Option is A, B

To understand the behavior of dynamic viscosity with temperature changes, let's look at both gases and liquids separately: 1. For gases:
- Dynamic viscosity (\(\mu\)) of gases typically increases with temperature. This happens because, as the temperature rises, the kinetic energy of gas molecules increases, leading to more frequent collisions between the molecules. These collisions result in a greater resistance to flow, which manifests as an increase in viscosity. - Mathematically, the viscosity of a gas is generally given by an equation of the form:
\[ \mu = A \cdot T^n \] where \(A\) and \(n\) are constants, and \(T\) is the absolute temperature. The exponent \(n\) is typically greater than 1 for most gases, indicating an increase in viscosity with temperature. - Therefore, the correct statement for gases is that the dynamic viscosity increases as the temperature increases. This corresponds to (A). 2. For liquids:
- Dynamic viscosity (\(\mu\)) of liquids generally decreases with temperature. As temperature increases, the liquid molecules gain more energy, which allows them to move more freely, reducing the internal friction or viscosity.
- For most liquids, the viscosity-temperature relationship is inverse to that of gases, meaning as the temperature increases, the liquid becomes less resistant to flow.
- This is particularly true for liquids like water, oil, and alcohol. For example, heating oil makes it flow more easily. Therefore, the correct answer is (A): "The dynamic viscosity of a gas increases."