## Tuesday, October 23, 2007

### IIT JEE Study Guide H C Verma JEE Physics Ch. 14 SOME MECHANICAL PROPERTIES OF MATTER

JEE syllabus
Hooke’s law 14.5,
Young’s modulus 14.5, 14.8

Viscosity (Poiseuille's equation excluded) (14.15),
Stoke's law (14.17);
Terminal velocity(14.18),
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Sections in the Chapter

1. Molecular structure of the material
2. Elasticity
3. Stress
4. Strain
5. Hooke's law & Young's modulus
6. Relation between longitudinal stress and strain
7. Elastic potential energy of a strained body
8 Determination of Young's modulus
9. Surface tension
10. Surface energy
11. Excess pressure inside a drop
12. Excess pressure in a soap bubble
13. Contact angle
14. Rise of a liquid in a capillary tube
15. Viscosity
16. Flow through a narrow tube: Poiseuille's equation
17. Stokes law
18. Terminal velocity
19. Measuring coefficient of viscosity by Stokes' method
20. Critical velocity and Reynold's number

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Study Plan

Day 1

1. Molecular structure of the material
2. Elasticity
3. Stress
Ex. 14.1

Day 2
4. Strain
5. Hooke's law & Young's modulus
Ex. 14.2
Worked Out Examples 1 to 3

Day 3
6. Relation between longitudinal stress and strain
7. Elastic potential energy of a strained body
Ex. 14.3
WOE 4
Exercises 1 to 5

Day 4
8 Determination of Young's modulus
9. Surface tension
Ex.14.4
10. Surface energy
Ex. 14.5
WOE 5,6

Day 5
WOE 7 to 10
Exercises 6 to 10

Day 6
11. Excess pressure inside a drop
12. Excess pressure in a soap bubble
13. Contact angle
14. Rise of a liquid in a capillary tube
WOE 11,12

Day 7
15. Viscosity
16. Flow through a narrow tube: Poiseuille's equation
17. Stokes law
WOE 13,14

Day 8
18. Terminal velocity
19. Measuring coefficient of viscosity by Stokes' method
20. Critical velocity and Reynold's number
WOE 15 to 17

Day 9

Exercises 11 to 20

Day 10
Exercises: 21 to 30

Revision Period: 30 minutes

Day 11
Exercises: 31,32
Objective I: 1 to 15

Day 12
Objective I: 16 to 29

Day 13
Objective II: 7

Day 14
Questions for Short Answer: 1 to 10

Day 15
Questions for Short Answer: 11 to 18

Day 16
Concept review

Day 17
Formula review

Day 18 to 20 Revision and problems from test paper guides

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Some Important concepts

Hooke's law

If the deformation is small, the stress in a body is proportional to the corresponding strain.

Tensile stress/Tensile strain = Y.

Y is a constant for a given material. This ratio is called Young's modulus for the material.

Stokes law (Ch. 14.17)

The viscous force ating on a small sphere, falling through a medium is equal to 6πηrv, where r is the radius of the sphere, v is velocity of the sphere, and η is the coefficient of viscosity of the medium.

Terminal velocity (Ch 14.18)
The viscous force on a solid moving through a fluid is proportional to its velocity (see stokes law).

When a solid is dropped in a fluid, the forces acting on it are

a. weight W acting vertically downward.
b. the viscous force F acting vertically upward and tbe buoyancy force acting vertically upward.

Weight and buoyancy forces are constant but viscous force changes with velocity.

If initially velocity is zero, viscous force is zero and the body is accelerated due to the forces W-B. As the body accelerates and velocity increases, viscous forces keeps increasing and at a certain instant it becomes equal to W-B. the net force becomes zero at that point and then onwards solid falls with constant velocity.