PHYSICS PART 2

Assignment 17

SHORT QUESTIONS

1. Distinguish between Soft magnetic materials and hard magnetic materials?

2. Define the modulus of elasticity. Show that units of modulus of elasticity and stress are the same.
3. What is difference between intrinsic and extrinsic semi-conductors?
4. Differentiate critical temperature from Curie temperature.
5. Distinguish between a valence band and conduction band.
6. Distinguish between polymeric solids and amorphous solids?
7. What is critical temperature? What is its value for lead?
8. Define unit cell and give the number of basic crystal systems.
9. What is the difference between Young’s modulus and bulk modulus?
10. Define super conductor and critical temperature.
11. Differentiate among diamagnetic, paramagnetic and ferromagnetic substances. Give two examples of each.
12. Explain briefly the substances on the basis of energy band theory.
13. What is meant by hysteresis loss? How is it used in the construction of a transformer?
14. What is meant by strain energy?
15. Define stress and strain with units. Give its types.
16. Define modulus of elasticity. Give its types.
17. What are glassy solids? Do they possess property of flow?
18. Distinguish between donor atoms and acceptor atoms.
19. Define Elastic limit and Yield point.
20. Differentiate between Brittle and Ductile materials
21. Describe the energy band picture of semiconductor.

LONG QUESTIONS

1. Write brief note on Energy band theory, How can you distinguish between conductor, semiconductor and insulator on
basis of energy band theory
2. What is meant by doping? Describe the formation of n-type and p-type semi-conductors?
3. What is meant by Hysteresis? Describe the different features of hysteresis loop.

PROBLEMS
1. A wire 2.5 m long and cross-sectional area is 10-5 m2 is stretched 1.5 mm by a force of 100 N in the elastic limit.
Calculate (i) the strain (ii) Young’s modulus.
2. A 1.25 cm diameter cylinder is subjected to a load of 2500 kg. Calculate the stress on the bar in mega Pascal.
3. A 1.0 m long copper wire is subjected to stretching force and its length increases by 20 cm. calculate the tensile strain
and the percent elongation which the wire undergoes
4. What stress would cause a wire to increase in length by 0.01% if the young’s modulus of the wire is 12×10 10 Pa. What
force would produce this stress if the diameter of the wire is 0.56 mm?

OBJECTIVE PART

1. Glass and high carbon steel are example of:

(a) Brittle substances (b) Ductile substances (c) Soft substances (d) Polymeric substances
2. The curie temperature of iron is:
(a) 750°C (b) 700°C (c) 3000°C (d) 1000°C
3. Good conductors have the conductivities of the order of:
(a) 10-7 (Ω-m)-1 (b) 107 (Ω-m)-1 (c) 102 (Ω-m)-1 (d) 10-2 (Ω-m)-1
4. How many crystals are there on the basis of geometrical arrangement of atoms?
(a) 3 (b) 5 (c) 4 (d) 7
5. The stress that produces change in shape is known as:
(a) Tensile stress (b) Shear stress (c) Volume stress (d) Longitudinal stress
6. The critical temperature for mercury is:
(a) 7.2 K (b) 4.2 K (c) 1.18 K (d) 3.7 K
7. Magnetism lags behind the magnetizing current, this phenomena is called:
(a) Coercivity (b) Hysteresis (c) Retentivity (d) Saturation
8. Substances with conductivities between 10-10 to 10-20 (Ωm)-1 are called:
(a) Superconductors (b) Insulators (c) Semi-conductors (d) Conductors
9. The ratio of applied stress to volumetric strain is called:
(a) Young’s modulus (b) Shear modulus (c) Bulk modulus (d) Tensile modulus
10. Domain contains atoms nearly:
(a) 103 to 106 (b) 1o12 to 1016 (c) 109 to 1010 (d) 106 to 109
11. Nm-2 is also called:
(a) tesla (b) weber (c) pascal (d) guass
12. The S.I units of stress are the same as that of:
(a) Momentum (b) Pressure (c) Force (d) Length
13. The substances with conductivities of the order of 10-6 (Ω-m)-1 to 10-4(Ω-m)-1 are:
(a) Conductors (b)Insulators (c) Semi-conductors (d) Super conductor
14. The ratio of applied stress to tensile strain is called as:
(a) Young’s modulus (b) Bulk modulus (c) Shear modulus (d) All of these
15. Which one of the following is polymeric solid?
(a) Iron (b) Nylon (c) Sodium (d) Zirconia
16. Domains exist in ---------materials:
(a) Ferromagnetic (b) Diamagnetic (c) Paramagnetic (d) Semi-conductor
17. The reciprocal of bulk modulus is:
(a) Tensile stress (b) Shear stress (c) Volume stress (d) Compressibility.
18. Area under the force extension graph for linear and non linear parts, is numerically equal to:
(a) Strain energy only for linear part (b) Strain energy only for non-linear parts
(c) Strain energy for both linear and non-linear parts (d) None of these
19. Which material has only bulk modulus?
(a) Concrete (b) Water (c) Mercury (d) Both B & C
20. With rise in heat and temperature, conductivity of semi-conductor
(a) Increases exponentially (b) Decreases exponentially (c) Decreases initially (d) None of these
21. The first super conductor was discovered by:
(a) J. J. Thomson (b) Kamerlingh Ornes (c) Michel Faraday (d) Ohm
22. For linear deformation, the ratio of tensile stress to tensile strain is given as:
(a) Bulk modulus (b) Young’s modulus (c) Normal modulus (d) Shear modulus
23. Forbidden energy gap in insulators is of the order of:
(a) 10 eV (b) 100 eV (c) 1000 eV (d) 0 eV
24. Glass solids have:
(a) Super temperature (b) Solid temperature (c) No definite melting point (d) None
25. Which metal is most suitable to make permanent magnet?
(a) Soft iron (b) Copper (c) Steel (d) Any of these.
26. Which material shows ductility:
(a) Lead (b) Glass (c) High carbon steel (d) Si thin waffer
27. Pentavalent impurity is:
(a) Boron (b) Aluminum (c)Indium (d) Phosphorus
28. The formula for the natural rubber is:
(a) (C4H6)n (b) (C6H4)n (c) (C5H6)n (d) (C3H6)n
29. The word amorphous means:
(a) Without form (b) Proper arrangement of atoms (c) Particular form (d) None
30. The maximum stress that a body can bear without break is called:
(a) Elastic limit (b) Yield stress (c) UTS (d) Fracture stress
31. Large area of hysteresis loop is due to:
(a) Large loss in energy (b) Large gain in energy (c) Small loss in energy (d) Small gain in
energy
32. Material still shows magnetism on magnetizing current being zero. It is called:
(a) Saturation (b) Coercivity (c)Retantivity (c) Any of these
33. High temperature superconductor has critical temperature:
(a) Greater than 77 K (b) Less than 77 K (c) Equal to 77 K (d) Zero K
34. The origin of magnetic field is:
(a) Orbital motion of electron (b) Spin motion of electron (c) Linear motion of electron (d) Both A &
B
35. Which of the following is not example of diamagnetic substances:
(a) Nickel (b) Copper (c) Water (d) Bismuth
36. Two copper wires have lengths in the ratio 1:2 and radii in the ratio 2:1, their Young’s modulus are in the ratio:
(a) 1:1 (b) 1:2 (c) 2:1 (d) 8:1
37. The core of transformer is made from:
(a) Soft iron (b) Alnico (c) Steel (d) Cobalt
38. The structure of unit cell is of:
(a) One dimension (b) Two dimension (c) Three dimension (d) Zero dimension
Prof. Muhammad Kashif
Punjab College, Faisalabad
0333-6543560