Liquid Test - 5

The boiling point at pressure 1 atm is known as normal boiling point. Normal boiling point is slightly greater than the standard boiling point as molecules change into the vapor phase and density of vapor increases.

Poise is the unit of viscosity. It’s S.I. unit is 1 Newton second per square meter. It’s Pascal second. In C.G.S. system, the unit of viscosity is poise that is named after a scientist Jean Louise Poiseuille. So, it’s 1 poise = 0.1 kgm^-1s^-1.

As there is a rise in temperature the viscosity of liquid increases while the viscosity of gas decreases. In liquids, due to rise in temperature, molecules have high thermal energy so the can overcome intermolecular attractions.

The formula of force required to maintain the flow of layers is given by the formula F = ηAdu/dz, where η is the coefficient of viscosity, A is the area of contact and du/dz is the velocity gradient. So by substituting we get an answer as 0.25dz/du.

The type of flow in liquids when each path flows in a different path, that do not interfere with each other is laminar flow. At any point in the fluid, the velocity of a fluid is constant is a characteristic of laminar flow.

Surface Tension is the tendency of a fluid to occupy least surface area as possible. It is defined as the force per unit distance. So, the units of surface tension are Newton/meter in S.I. the system, Dyne/cm in C.G.S system.

When the angle of contact between the liquid and container is 90 degrees then the cohesive and adhesive forces in a liquid are equal. Cohesive force is the attraction between similar atoms and adhesive between different atoms.

Surface Tension is the tendency of a fluid to occupy least surface area as possible. It is defined as the force per unit distance. So, the spherical shape that is acquired by a water drop is due to surface tension.

The surface tension in liquids decreases with rise in temperature. As surface tension decreases, molecules become more active when temperature increases and surface tension becomes zero at critical temperature T_C.

Viscosity in general is a fluid’s (gas or liquid) resistance to flow .

A is correct, high viscosity implies more resitance to flow, therefore slower is liquid flow.

B is wrong, fluid viscosity may increase or decrease with increase in temperature

C is wrong as stronger bonds means less tendency to flow i.e. higher viscosity.

D is wrong, its opposite of viscosity, viscosity is the resitance against flow, not the ease with which a liquid flows.