Tag: viscosity

Questions Related to viscosity

Viscosity is most closely related to:

viscosity option b: engineering physics properties of matter physics

  1. density

  2. velocity

  3. friction

  4. energy

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Correct Option: C
Explanation:

Viscosity is the property by virtue of which a liquid offers resistance for the relative motion between liquid molecules. Friction is the force which opposes relative motion between any two objects. So, viscosity is most closely related to friction.

Viscosity of the fluids is analogous to:

viscosity option b: engineering physics properties of matter physics

  1. Random motion of the gas molecules

  2. Friction between the solid surfaces

  3. integral motion

  4. Nonuniform motion of solids

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Correct Option: B
Explanation:

Viscosity is the property by virtue of which a liquid offers resistance for the relative motion between its layer.
Friction is the force between two solid surfaces which offers resistance for the relative motion between them. 
So, viscosity of the fluids is analogous to friction between the solid surfaces.

The main cause of viscosity is:

viscosity option b: engineering physics properties of matter physics

  1. force of repulsion between molecules.

  2. cohesive forces.

  3. adhesive forces.

  4. both cohesive and adhesive forces.

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Correct Option: B
Explanation:

When the inter-molecular forces of attraction are strong within a liquid, there is a viscosity. Cohesive forces are attractive forces exist between molecules of the same substance. So, cohesive forces are the main cause of viscosity. Adhesive forces are attractive force between unlike molecules.

The arrow with a pointed tip can move faster in air than that of with a blunt tip.

viscosity option b: engineering physics properties of matter physics

  1. True

  2. False

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Correct Option: A
Explanation:

The arrow with  a pointed tip can move faster in air than that of with a blunt tip because blunt tip arrow has more area of cross section , so it requires more amount of force to create the same amount of pressure as that by the pointed tip .

so given statement is true  , hence option (A) is correct

Viscosity is the property by virtue of which a liquid:

viscosity option b: engineering physics properties of matter physics

  1. occupies minimum surface area.

  2. offers resistance for the relative motion between its layers.

  3. becomes spherical in shape.

  4. tends to gain its deformed position.

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Correct Option: B
Explanation:

Viscosity is the property by virtue of which a liquid offers resistance for the relative motion between it's layer because it's main cause is cohesive force which acts between like molecules and try to bind them. So, it offers resistance for relative motion between liquid molecules.

The cause of viscosity of liquid is:

viscosity option b: engineering physics properties of matter physics

  1. diffusion.

  2. adhesive force.

  3. gravitational force.

  4. cohesive force.

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Correct Option: D
Explanation:

Due to strong cohesive forces between the molecules, any layer in a moving fluid tries to drag the adjacent layer to move with an equal speed and thus produces the effect of viscosity.

Viscosity is exhibited by:

viscosity option b: engineering physics properties of matter physics

  1. Solids, liquids, and gases.

  2. liquids and gases

  3. Solids and gases

  4. Solids and liquids

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Correct Option: B
Explanation:

Viscosity is exhibited by liquids and gases only. In solids, the role of viscosity is played by friction. 

Aeroplanes are streamlined to reduce ....................... friction.

viscosity option b: engineering physics properties of matter physics

  1. Contact

  2. Fluid

  3. Both (A) and (B)

  4. None

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Correct Option: B
Explanation:

To reduce the fluid  friction body of an Aeroplane is streamlined .

so option (B) is correct

The dimensions of velocity gradient are:

viscosity option b: engineering physics properties of matter physics

  1. [$T^{-1}$]

  2. [$T$]

  3. [$T^2$]

  4. [$T^{\circ}$]

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Correct Option: A
Explanation:


Velocity gradient $=\dfrac{dv}{dx}$
so dimensions of velocity gradient is $\dfrac{[LT^{-1}]}{[L]}=[T^{-1}]$

The viscous drag is:

viscosity option b: engineering physics properties of matter physics

  1. inversely proportional to the velocity gradient.

  2. directly proportional to the surface area of layers in contact.

  3. independent of nature of liquid.

  4. perpendicular to the direction of liquid flow.

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Correct Option: B
Explanation:

The viscous drag force can be written as below:
$F =  \eta \ A \ (\cfrac{dV}{dX})$ where, F is viscous drag force (or tangential force)
$\eta$ is coefficient of viscosity
$A$ is surface area of layers in contact
$\dfrac{dV}{dX} $ is velocity gradient
$\eta$ is property of liquid.
So, we can see that drag is directly proportional to the velocity gradient, surface area and nature of liquid. Drag force acts in opposite direction of liquid flow.