Class 11 Physics Important Chapter 10 Mechanical Properties of Fluids

Class 11 Physics Important Chapter 10 Mechanical Properties of Fluids Solutions English Medium As Per AHSEC New Syllabus to each chapter is provided in the list so that you can easily browse through different chapters NCERT Class 11 Physics Important Solutions and select need one. AHSEC Class 11 Physics Additional Notes English Medium Download PDF. HS 1st Year Physics Important Solutions in English.

Class 11 Physics Important Chapter 10 Mechanical Properties of Fluids

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Mechanical Properties of Fluids

Chapter: 10

IMPORTANT QUESTION AND ANSWER

Answer the Following Questions:

1. Define fluid.

Ans: “A fluid is a substance (liquid or gas) that can flow. Liquids have definite volume but no fixed shape, while gases have neither fixed shape nor fixed volume.”

2. What is atmospheric pressure?

Ans: It is the pressure exerted by the weight of the air in the atmosphere at sea level, approximately 1.013 × 10⁵ Pa.

3. State Pascal’s law in fluids.

Ans: Pressure applied to an enclosed fluid is transmitted undiminished in all directions throughout the fluid.

4. Write the equation for pressure variation with depth in a fluid.

Ans: P = P_a + pgh.

5. What is viscosity?

Ans: Viscosity is the internal friction in a fluid that opposes relative motion between its layers.

6. What is the SI unit of viscosity?

Ans: Pascal-second (Pa·s) or N·s/m².

7. What is streamline flow?

Ans: Flow where fluid particles follow smooth paths or streamlines that do not intersect.

8. Write Bernoulli’s equation.

Ans: P + ½ ρv² + ρgh constant.

9. What is surface tension?

Ans: Surface tension is the force per unit length along the surface of a liquid, due to molecular attraction.

10. Why do fluids exert pressure perpendicular to surfaces?

Ans: Because any tangential component would cause fluid motion; fluids at rest exert pressure only normal to surfaces.

Short Type Question and Answer:

1. What is pressure in fluids? State Pascal’s law and explain its applications.

Ans: Pressure in a fluid is the force exerted normally (perpendicular) per unit area on a surface within the fluid.

Mathematically,

P = F/A

where F is the force and A is the area.

Pascal’s Law:

In a fluid at rest, the pressure is transmitted equally and undiminished in all directions at the same depth. This means any change in pressure applied to a confined fluid is transmitted throughout the fluid.

Applications:

Hydraulic lift and brakes, where small force applied on a small piston is transmitted to generate a large force on a bigger piston.

Devices like syringes and car lifts.

2. Explain how pressure varies with depth in a fluid and derive the formula for pressure at a depth.

Ans: In a fluid at rest, pressure increases with depth due to the weight of the fluid above.

Consider a column of fluid of height hhh, cross-sectional area A, and density ρ. The weight of fluid column is mg = ρVg = ρAhg.

The difference in pressure between the bottom and the top of the column is the weight per unit area:

P₂ − P₁ = mg / A = ρgh

If the surface is open to the atmosphere, pressure at the surface is atmospheric pressure Pa​, so pressure at depth h is:

P = P_a + ρgh

3. State Bernoulli’s principle and explain its significance in fluid flow.

Ans: Bernoulli’s principle states that for an incompressible, non-viscous fluid flowing steadily, the sum of the pressure energy, kinetic energy per unit volume, and potential energy per unit volume remains constant along a streamline. Mathematically,

P + ½ PV² + Pgh = constant

This means if the velocity of fluid increases, the pressure decreases, and vice versa.

Significance:

Explains why airplane wings produce lift (dynamic lift).

Helps understand flow speed changes in pipes of varying cross-sections.

Explains the working of carburetors, atomizers, and venturi meters.

4. Define viscosity. How does viscosity affect fluid flow? Explain Stokes’ law.

Ans: Viscosity is the property of a fluid that offers resistance to its flow or motion between layers, like internal friction.

Viscosity causes energy loss due to friction between fluid layers flowing at different velocities, making flow slower and converting some kinetic energy into heat.

Stokes’ Law:

For a sphere of radius aaa moving at velocity v in a fluid with viscosity η the viscous drag force is:

F = 6 πηav