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Chapter 17 Physics Of Solids Physics 12th Class Punjab Short Questions

Question No. 1 - What is the difference between intrinsic and extrinsic semiconductors?

Answer No. 1 - Intrinsic Semiconductor: A semiconductor in its extremely pure form is known as Intrinsic semiconductors, Pure elements of silicon and germanium are Intrinsic semiconductors. These semiconductors elements have atoms with four valence electrons.

Question No. 2 - Define polymeric solid with example.

Answer No. 2 - Polymers are solid materials with a structure that is intermediate between order and disorder. They can be classified as partially or poorly crystalline solids. For example plastic, rubber.

Question No. 3 - Differentiate between ductile and brittle substance, Give their examples.

Answer No. 3 - Ductile substance: Substance that undergo plastic deformation unit they break are called ductile substance. Lead copper and wrought iron are ductile.
Brittle substance: The substance which break just after the elastic limit reached are known as brittle substance. Glass and high carbon steel are brittle.

Question No. 4 - What are paramagnetic Substance? Give an example.

Answer No. 4 - The solid in which the orbital and spin axes of the electrons in an atom are so oriented that their magnetic field support each other are called paramagnetic substance. For example ozone, platinum etc.

Question No. 5 - Distinguished between elasticity and plasticity.

Answer No. 5 - Elasticity: In deformed crystalline solid, the atoms return to their equilibrium position after the removal of external force. This ability of the body to return to its original shape is called elasticity.

Question No. 6 - Define retantivity.

Answer No. 6 - When the current is reduced to zero, the material still remains strongly magnetized which is known as retantivity.

Question No. 7 - Write the used of superconductors.

Answer No. 7 - Superconductors can be used in :
1. Magnetic Resonance Imaging
2. Powerful but small electric motors
3. Fast computer chips
4. Magnetic Levitation Trains

Question No. 8 - What are glassy solids? Do they possessed property of flow?

Answer No. 8 - Amorphous solids are called as glassy solids. Any non-crystalline solid in which the atoms and molecules are not organized in a definite lattice pattern is called glassy solid. NO they do not possess the property of flow.

Question No. 9 - Define UTS of a material.

Answer No. 9 - The maximum stress that a material can withstand is called ultimate tensile stress.

Question No. 10 - Define young modulus and shear modulus.

Answer No. 10 - The ratio of tensile stress to tensile strain is called young modulus.

Question No. 11 - Distinguished between a valence and a conduction band.

Answer No. 11 - Valence bond: The energy band occupied by valence electrons is called the valence band.

Question No. 12 - Describe the energy band picture of semiconductors.

Answer No. 12 - In semiconductors, valence band and conduction is partially filled and they have a very narrow forbidden energy gap.

Question No. 13 - Define Polymerization. Write two examples of polymeric solid?

Answer No. 13 - Polymers are found by polymerization reaction. In these reaction relatively simple molecule are chemically combined into massive long chain molecule or three dimensional structure.
Polythene and nylon are example of polymeric solids.

Question No. 14 - How can the strain energy be determined from the force extension graph?

Answer No. 14 - Strain energy can be determined from the force extension graph according to the following relation:
Strain Energy : 1/2 l1F1

Question No. 15 - Define crystalline and amorphous.

Answer No. 15 - Crystalline: The solid in which there is a regular and periodic arrangements of the atoms and molecule are crystalline solids.
Amorphous: The solid in which there is no regular arrangement of molecules like that in crystalline solids are called amorphous solid. For Example; Ordinary Glass.

Question No. 16 - What does are of hysteresis loop tell?

Answer No. 16 - The area of the loop is the measure of the energy needed it magnetize and demagnetize the specimen during each cycle of the magnetizing current. This is the energy required to do work against internal friction of the domains. This work is dissipated as heat. It is called hysteresis loss.

Question No. 17 - Define cell unit.

Answer No. 17 - A crystalline solid consists of three dimensional pattern that repeat itself over and over again. This smallest three dimensional basic structure is called unit cell.

Question No. 18 - Define superconductors.

Answer No. 18 - The materials whose resistivity becomes zero below a certain temperature are called superconductors. For example mercury becomes super conductor below 4.2 K temperature.

Question No. 19 - How n type semiconductors are formed?

Answer No. 19 - When a silicon crystal is doped with a pentavalent element, e.g arsenic, antimony or phosphorus etc. Four valence electrons of the impurity atom form covalent bond with the four neighbouring Si atoms, while the fifth valence electrons provide a free electron in the crystal. Such a doped semiconductor is called n type semiconductor.

Question No. 20 - Define insulators, conductors and semiconductors.

Answer No. 20 - Insulator: Those substance which have valence electrons tightly bound to their atoms are called insulators.
Conductors: Those substance which have plenty of free electrons for electrical conduction are called conductors.
Semiconductors: Those substance which have intermediate range of conductivity are called semiconductors e.g germanium and silicon.

Question No. 21 - Distinguished between P-type semiconductor and N-type semiconductor.

Answer No. 21 - P-Type Semiconductor: When a trivalent impurity such as aluminium is added into the semiconductor, holes are generated and P-Type Semiconductor is formed. Holes are positive charge carrier.

Question No. 22 - Describe energy band picture of insulators.

Answer No. 22 - Insulators are those materials in which valence electron are bound to very tight to their atoms and are not free. In terms of energy bands, it means that an insulator has:
. An empty conduction band
. A full valence band
. A large energy gap

Question No. 23 - Define Saturation and Remanence of Hysteresis Loop.

Answer No. 23 - Saturation: The material is said is reduced to magnetically saturated when magnetic flux density reaches a maximum value.
Remanence: When the current is reduced to zero, the material still remains strongly magnetize. It is due to the tendency of domains to stay partly in line, once they have been aligned. It is called remanence or relativity.

Question No. 24 - Define Fracture stress.

Answer No. 24 - Once the limit of ultimate tensile stress UTS is crossed, the material breaks and the stress is called fracture stress.

Question No. 25 - Define volumetric strain.

Answer No. 25 - When the applied stress change the volume, then the change in volume per unit volume is called volumetric strain.

Question No. 26 - Define coercivity of a material.

Answer No. 26 - To demagnetize the material the magnetizing current is reserved and increased to reduce the magnetization to zero. This is known as coercive current and this process is called coercivity.

Question No. 27 - What is meant by strain energy? How can it be determined from the force extension of graph?

Answer No. 27 - The amount of P.E stored in a material due to displacement of its molecule from its equilibrium position under the action of stress is called strain energy. Strain energy can be determined from the force extension graph according to the following reasons:
Strain Energy = 1/2L1F1

Question No. 28 - Differentiate between tensile stress and shear modes of stress and strain.

Answer No. 28 - Tensile Stress: A stress that cause the change in length of an object is called tensile stress.
Shear Stress: A stress that cause the change in shape of an object is called shear stress.
Tensile Stain: If the strain is due to tensile stress it is called tensile strain. A strain produced in the object when it is subjected to shear stress is called shear strain.

Question No. 29 - Describe the difference between proportional limit and elastic limit.

Answer No. 29 - Proportional Limit: The greatest stress that a material can endure without losing straight line proportionally between stress and strain. Hookes law is obeyed in this region.

Question No. 30 - Define stress and write its formula.

Answer No. 30 - It is defined as the force applied on unit are to produce any change in shape, volume or length of a body. Its formula is
Stress = Force/Area

Question No. 31 - How the conductivity of semiconductor can be raised?

Answer No. 31 - The conductivity of a semiconductor can be raised by the process of doping in which small number of impurity atoms are added to pure semiconductors.

Question No. 32 - Define stress and strain, What are their units.

Answer No. 32 - The force applied on unit area to produce any change in the shape, volume or length of the body is called stress, its SI units is pascal.
And strain is the measure of deformation of solid when stress is applied to it. It has no unit.

Question No. 33 - Differentiate between amorphous and polymeric solid.

Answer No. 33 - Amorphous solid,any non-crystalline solid in which the atoms and molecules are not organized in a definite lattice pattern, such solid include glass, plastic and gel.

Question No. 34 - Define elastic limit and Yield point.

Answer No. 34 - The greatest stress that a material can endure without any permanent deformation is called elastic limit. This kind of behavior is called elasticity.
Yield point: The point on the stress-strain curve beyond which if stress is further increased then permanent deformation takes place in the given specimen. This is called yield point.

Question No. 35 - What is meant by para and ferromagnetic substance?

Answer No. 35 - The orbits and the spin axes of the electrons in an atom are so oriented that their field spot each other and the atom behaves like a tiny magnet. Substance with such atoms are called paramagnetic substance e.g iron.
There are some solid substance in which the atom cooperate with each other in such a way so as to exhibit a strong magnetic field there are called ferromagnetic substance.

Question No. 36 - What is critical temperature in super conductivity?

Answer No. 36 - The temperature below which the resistivity of a material falls to zero is called critical temperature. For example Mercury.

Question No. 37 - Compare the electrical behavior of conductor and semiconductor in terms of energy band theory.

Answer No. 37 - On the basic of energy band theory In conductors, free electrons are available for conduction, Valence and conduction bands largely overlap each other and In semiconductors, valence band and conduction band is partially filled and they have a very narrow forbidden energy gap.

Question No. 38 - What is meant by strain energy?

Answer No. 38 - The amount of P.E stored in a material due to displacement of its molecule from its equilibrium position under the action of stress is called strain energy. Strain energy can be determined from the force extension graph according to the following reasons:

Strain energy=1/2L₁F₁

Question No. 39 - What is meant by Ferromagnetic Substance?

Answer No. 39 - In ferromagnetic substance the atoms cooperate with each other in such a away so as to exhibit a strong magnetic field. In ferromagnetic substance there exists a small region called domain.

Question No. 40 - Explain what is curie temperature?

Answer No. 40 - The temperature at which the domains of ferromagnetic material start losing their orderliness is called Curie temperature. For example the curie temperature of iron is 750°C.

Question No. 41 - Distinguished between soft magnetic material and hard magnetic materials.

Answer No. 41 - Soft Magnetic: The materials in which their domains can be easily orientated on applying external magnetic field and also return to original positions when field is removes. E.g iron.

Question No. 42 - What is meant by hysteresis loss?

Answer No. 42 - The area of the loop is the measure of the energy needed to magnetize and demagnetize the specimen during each cycle of the magnetizing current. This is energy required to do work against internal friction of the domains, this work is dissipated as heat. It is called hysteresis loss.

Question No. 43 - Define module of elasticity.

Answer No. 43 - The ratio of stress to strain is constant for a given material, provided the external applied force is not too great called modulus of elasticity.
Modulus of Elasticity = Stress/Strain

Question No. 44 - Define crystal lattice.

Answer No. 44 - The whole structure obtained by the repetition of unit cell is known as crystal lattice.

Question No. 45 - Define yield point and ultimate tensile stress.

Answer No. 45 - Yield Point: The point on the stress-strain curve beyond which if stress is further increased then permanent deformation takes place in the given specimen. This is called yield point.
Ultimate Tensile Stress: The maximum stress that a material can withstand called ultimate tensile stress.

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