FSc ICS Notes Physics XII Short Questions & Definitions Chapter 17 Physics of Solids

FSc ICS Notes Physics XII Short Questions & Definitions Chapter 17 Physics of Solids 2nd Year Physics Notes Online Taleem Ilmi Hub

If you want to view Exercise Question & Numerical Problems. Please refer to this page Physics Part 2

Material: Of or pertaining to matter or substance; formed or consisting of matter.

Matter: Any material object composed of molecules, which is solid, liquid, or gaseous, and that occupies space and can effect one or more of our senses.

Hardness: The resistance that a face of the crystal offers to scratching, which may differ in different directions. For many substances, hardness is an inverse measure of plasticity.

Ductility:

• The property of a metal which can be drawn through a die to produce a wire.
• Ability of a substance to be drawn into fine wires.

Malleability: The property of a metal, which can be hammered or rolled into sheets.

Electrical conductivity: The ability of a material to conduct electric current; the reciprocal of the resistivity.

Thermal conductivity: A measure of the ability of a material to conduct energy.

Bonding of atoms: A strong force of attraction holding atoms together in a molecule or crystal.

Crystalline: Having a regular arrangement of particles.

Crystalline solids: Solids with a definite, fixed melting point.

Molecule: A single atom or a group of atoms joined by chemical bonds. It is the smallest unit of a chemical compound that can have an independent existence.

Solid: The state of matter, which has definite volume and definite shape.

Solidification: The change of state from a liquid to a solid.

Ceramics: Inorganic materials, such as pottery, enamels, and refractories.

Production of X-rays (or Inverse photoelectric effect): The emission of photons of radiations due to the bombardment on a material with high speed electrons.

X-rays:

• Invisible penetrating radiation of great penetrating power.
• Electromagnetic radiation of extremely short wavelength.

Adhesion:

• The force of attraction between unlike molecules.
• The interaction between the surfaces of two closely adjacent bodies that causes them to cling together.

Cohesion:

• The force of attraction between like molecules.
• The tendency of the different parts of a body to maintain their relative positions unchanged.

Cohesive forces: The forces of attraction between the particles, e.g., atoms, molecules, or ions, in crystalline solids.

Melting point: The temperature at which a solid changes to a liquid.

Ice point: The temperature of melting ice, 0o C.

Amorphous solids (or Glassy solids): Solids having a random arrangement of particles; non-crystalline solids.

Polymer: A substance having large molecules consisting of repeated units. Synthetic polymers are extensively used in plastics.

Synthetic: Describing a substance that has been made artificially; i.e. one that does not come from a natural source.

Synthetic materials: Materials that are made artificially.

Synthetic rubber: Artificially made rubber.

PVC (Polyvinyl chloride or Polychloroethene): A tough white solid material, which softens with the application of a plasticizer. It is easy to colour and resistant to fire, chemicals, and weather.

Plasticizer: A substance added to a synthetic resin to make it flexible.

Resin: A synthetic or naturally occurring polymer.

Polythene (Polyethene or Polyethylene): A flexible waxy translucent thermoplastic made in a variety of ways producing a polymer of varying characteristics.

Translucent: Semi-transparent or capable of letting light through so as to allow objects to be indistinctly visible.

Polystyrene: A clear glasslike material used as both a thermal and electrical insulator and for packing and decorative purposes.

Nylon: Any of various synthetic thermoplastic polymers whose molecules are linear polyamides, many of which are tough, lightweight, and resistant to heat and chemicals, and may be produced as filaments (widely used in textiles) or sheets, or as moulded objects.

Hydrocarbon: Chemical compounds that contain only carbon and hydrogen.

Crystal lattice (or Lattice): A regular periodic repeated three-dimensional array of points that specify the positions of atoms, molecules, or ions in a crystal.

Unit cell: Smallest crystal unit possessing the entire symmetry of whole periodic structure.

Squeeze: An application of strong or firm pressure.

Inter atomic cohesive force: The force of attraction between like atoms in crystalline solids.

Elasticity: The property of a material body to regain its original condition, on the removal of the deforming forces.

Stress: The distorting force per unit area set up inside the body.

Strain: The change produced in the dimensions

Tensile stress: The stress tending to stretch a body.

Compressive stress (or Bulk stress): It is an overall force per unit area (pressure) applied.

Shear stress: It is a stress tending to produce an angular deformation. It is the tangential force per unit area.

Tensile strain: It is the change in length divided by the original length ( Δ l / l ). It applies to the stretching of a body; the strain produced as a result of tensile stress.

Compressive strain: The strain produced as a result of compressive stress.

Volumetric strain (or Bulk strain): It is the change in the volume divided by the original volume. It occurs when a body is subjected to a pressure.

Shear strain: It occurs when an angular deformation occurs, and is equal to the angular displacement produced.

Radian: The angle subtended at the center of a circle by an arc equal in length to its radius.

Elasticity: The property of a material body to regain its original condition, on the removal of the deforming forces.

Modulus of elasticity (or Elastic modulus): The ratio of the stress on a body to the strain produced. There are various modulii of elasticity depending on the type of stress applied.

Young’s modulus: Linear elasticity, or elasticity of length.

Bulk modulus: Elasticity of volume, corresponding to volume strain.

Shear modulus: The ratio of the shear stress on a body to the shear strain produced.

Elastic constant: Such as Young’s modulus, relating stress to strain in a homogeneous medium. For an isotropic material, two constants are required to specify the behaviour and these are related by linear equations. In general, an anisotropic solid is described by 21 elastic constants.

Isotropy: A medium is isotropic if the value of a measured physical quantity does not depend on the direction.

Anisotropy: A medium is anisotropic if a certain physical quantity differs in value in different directions. Most crystals are anisotropic electrically; polarization properties result from differences in transmission of electromagnetic radiation in different directions.

Tensile test: Measuring the extension of a metal wire at a specified deformation rate and the stresses generated during deformation, from a suitable electronic device fitted in the mechanical testing machine.

Ductility: Combination of properties of a material that enables it to be drawn out into wires.

Ductile material: Materials that have property, that enables it to be drawn out into wires.

Proportional limit: That point up to which a material obeys Hooke’s law. The strain produced is proportional to the stress and the sample returns to its original dimensions if the stress is removed.

Elastic limit: The point above the proportional limit where the material no longer obeys Hooke’s law.

Hooke’s law: Within the limits of perfect elasticity stress is directly proportional to strain.

Elastic deformation: Temporary deformation produced in a material, which can be regained to its original shape or dimensions, on removing the applied stress.

Yield stress: The minimum stress for creep to take place. Below this value any deformation produced by an external force will be purely elastic.

Creep: The slow permanent deformation of a crystal or other specimen under sustained stresses.

Plastics: Materials that, though stable in use at normal temperature, are plastic at some stage in their manufacture, and can be shaped by the application of heat and pressure.

Plasticity: The tendency of a material to suffer a permanent deformation; i.e. not to return to its original dimensions after a deforming stress has been removed. An elastic material becomes plastic above its yield point.

Yield point: The point at which the material begins to ‘flow’, i.e. the strain increases with time up to breaking point without further increase in the stress.

Ultimate strength: The limiting stress, in terms of force per original unit area of cross section, at which a material completely breaks down, fractures or crushes.

Ultimate tensile strength: The limiting change in length , in terms of force per original length, at which a material completely breaks down.

Fracture stress: The point where the material breaks after crossing the point in ultimate tensile stress.

Ultimate tensile stress: The maximum stress that a material can withstand; regarded as the normal strength of the material.

Ductile substances: Substances that undergo plastic deformation until they break.

Brittle substances: Substances that break just after the elastic limit is reached.

Elastic: A material that tends to resume its original size and shape after being subject to deforming stresses.

Diverse: Differing from itself in different circumstances, at different times, or in different parts; varied; changeful.

Strain energy: It is the potential energy stored in the body because of an elastic deformation, which is equal to the work done to produce this deformation.

Diamond: The hardest known mineral. It is an allotropic form of pure carbon that has crystallized in the cubic system under great pressure.

Carbon (6C): A nonmetallic element belonging to group IV of the periodic table. It has two main allotropic forms, diamond and graphite.

Semiconductor (or Semiconductor device): A material such as silicon or germanium that has a resistivity midway between that of conductors and that of insulators.

Silicon (14Si): An element having four electrons in its outermost shell called valence electrons. It is used in semiconductor devices in the form of single crystal.

Germanium (32Ge): A brittle metalloid, used as a semiconductor in solid-state electronic devices and as a constituent of alloys, phosphors, and infrared glasses.

Bohr model (or Bohr atomic model): It is based on the following three postulates:

1. An electron in an orbit around the nucleus does not radiate energy.
2. Only those orbits are possible for which the angular momentum of the electron is an integral multiple of h / 2π.
3. An electron does not emit light when it is moving in one of the allowed orbits. It emits light only when electron jumps from one orbit (outer) to another orbit (inner).

Free electron theory: The atoms have electrons revolving around the nucleus in orbits. In certain atoms, electrons in outer most orbits are loosely bound, called free electrons. A small amount of energy shell let these electrons leave the atom.

Energy band theory: The electrons in a solid have different energy levels. The electrons can exist in some ranges of permissible energy levels and cannot exist in other ranges of forbidden energy levels. The permissible levels taken in groups are called energy bands.

Wave mechanical model: The theory based upon Schrodinger’s wave equation.

Schrodinger’s wave equation: The equation of wave mechanics that gives mathematical expression to wave motion; Δ ψ + 8 π2 m (E + U) / h(square)= 0

Energy states: Energy levels around the nucleus of an atom in which electrons can exist.

Energy band: The permissible energy levels taken in groups called energy bands within which the levels are very close and they appear to be continuous.

Discrete: Taking only certain values; Separate, detached from others; individually distinct; not continuous; Consisting of or pertaining to distinct or individual parts of a magnitude or quantity.

Continuous energy band: Closely spaced permissible energy states in which electrons can exist.

Forbidden energy states: A range of energy states which cannot be occupied by electrons, found in between two consecutive permissible energy bands.

Valence electrons: Electrons in the outermost shell of an atom that are involved in chemical changes.

Conduction band: The band above the valence band. In it electrons move freely and conduct electric current through solids.

Valence band: Energy band occupying valence electrons in the outer most shell of an atom.

Insulator: A material through which an electric charge is not readily transferred.

Conductor: A material through which an electric charge is readily transferred.

Semi-conductor: A material such as silicon or germanium that has a resistivity midway between that of conductors and that of insulators.

Intrinsic semi-conductor: A pure semiconductor material. In it the concentrations of negative charge carriers (electrons) and positive charge carriers (holes) are the same.

Extrinsic semi-conductor: Such material in which certain impurities are added. Its conductivity increases considerably depending strongly on the type and concentration of the impurity.

Doping: The process of adding impurity to control the conductivity is called doping.

Chemical bond: A strong force of attraction holding atoms together in a molecule or crystal.

Ionic bonds: These bonds are formed by transfer of electrons.

Covalent bond: They are formed by sharing of valence electrons rather than by transfer.

Pentavalent element: The elements having a valency of five.

N-type semi-conductor (or N-type germanium): Electron rich semi-conductor (or germanium) consisting of equal number of free electrons and bound positive charges so that the net charge is zero.

P-type semi-conductor (or P-type germanium): “Hole rich” semi-conductor (or germanium) consisting of equal number of free positive holes and bound negative charges so that the net charge is zero.

Phosphorous (15P ): A nonmetallic element belonging to group IV of the periodic table. It is highly reactive. It is an essential element for living organisms.

Hole: In a solid, an empty state near the top of the valence band. Electrons can move into such empty states from adjacent occupied states, permitting the conduction of a current.

Free electron: An electron that is not permanently attached to a specific atom or molecule and is free to move under the influence of an applied electric field.

Electronic current: The current due to flow of electrons.

Conventional current: The current due to flow of an equivalent positive charge.

Superconductivity: The effective disappearance of electrical resistance in certain substances when they are cooled close to absolute zero. Currents induced in circuits of such materials have persisted for several years with no measurable change.

Superconductor: A substance having the properties of super conductivity.

Critical temperature (TC ): The upper limit of temperatures at which it is possible to have a substance in its liquid state.

Magnetic resonance imaging (MRI): A technique that is based on nuclear magnetic resonance of protons, and is used in diagnostic medicine to produce images (proton-density maps) of the body.

Nuclear magnetic resonance (NMR): An effect observed when radio-frequency radiation is absorbed by matter. A nucleus with a spin has a nuclear magnetic moment. In the presence of an external magnetic field this magnetic moment precesses about the field direction.

Precession: If a body is spinning on an axis, the axis of rotation can itself move around another axis at an angle to it.

Magnetic levitation train (or Maglev train): A high speed ground transportation vehicle levitated above a track called a guideway and propelled by magnetic fields. A short-distance maglev train has been operating since 1984 in England. Train speeds 517 km/h have been demonstrated in Japan.

Levitate: Cause something heavier to rise or remain suspended without visible means e.g. using magnetic forces.

Propel: Drive or push something forward, cause to move onwards.

Computer chip (or Chip): A small piece of single crystal of semiconductor material containing either a single electronic component or an integrated circuit.

Alloy: A mixture of two or more metals or of a metal with small amounts of non-metals.

Magnetic dipole: A pair of north-seeking and south-seeking magnetic poles a distance apart, as in a bar magnet.

Magnetic pole: Point in a magnet from which lines of force appear to radiate.

Magnetic moment (or Magnetic dipole moment): The torque experience by a magnetic dipole in a field of unit magnetic field strength perpendicular to it.

Para magnetism: Property of a substance by which it is feebly attracted by a strong magnet.

Diamagnetism: Property of a substance whereby it is feebly repelled by a strong magnet.

Ferromagnetism: The property of a substance by which it is strongly attracted by a magnet.

Paramagnetic substances: The substances in which, the orbits and the spin axes of the electrons in the atom are so oriented that their fields support each other and the atoms behaves like a tiny magnet.

Diamagnetic substances: The substances in whose atoms, there is no resultant field as the magnetic fields produced by both orbital and spin motions of the electrons might add up to zero.

Ferromagnetic substances: The substances in which, the atoms cooperate with each other in such a way so as to exhibit a strong magnetic effect.

Domain: A region inside a ferromagnetic material in which all the atomic magnetic fields point the same way.

Squid: (super-conducting quantum interference device) Any of a family of super-conducting devices that are capable of measuring extremely small magnetic fields, voltages, and currents.

Soft magnetic material: The material whose domains are easily oriented on applying an external field and readily return to random positions when field is removed.

Hard magnetic material: The material whose domains are not so easily oriented on applying an external field. They require very strong external fields, but once oriented, retain the alignment.

Curie temperature (or Curie point): The temperature above which a ferromagnetic substance loses its ferromagnetism.

Organic material: A material containing carbon combined with hydrogen, and often also with oxygen, and other elements.

Hysteresis (or Magnetic hysteresis) : The lagging of magnetization of ferromagnetic material behind the magnetizing force.

Hysteresis loop: The loop formed by magnetic hysteresis.

Magnetic flux density: Number of flux lines per unit perpendicular area of a magnetic field.

Remanence (or Retentivity):

• The residual magnetic flux density in a substance when the magnetizing field strength is returned to zero.
• When substances are applied forces for producing magnetization and then force removed then power of retaining their original magnetization is called retentivity.

Coercivity: Degree of reversed magnetizing force required to deprive the metal of the whole of its original magnetization.

Coercive force: The magnitude of coercicity.

Coercive current: The reversed magnetizing current required to reduce the magnetization in a material to zero.

Hysteresis loss: The dissipation of energy that occurs, due to magnetic hysteresis, when the magnetic material is subjected to cyclic changes of magnetization.

Polymeric solids: Solid substance having large molecules consisting of repeated units. Synthetic polymers are extensively used in plastics.

Intrinsic semi-conductor: A pure semiconductor material. In it concentrations of negative charge carriers (electrons) and positive charge carriers (holes) are the same.

Extrinsic semi-conductor: Such material in which certain impurities are added. Its conductivity increases considerably depending strongly on the type and concentration of the impurity.

Pascal: The SI unit of pressure, equal to a pressure of one Newton per square metre.

Written By: Asad Hussain