FSc ICS Notes Physics XII Short Questions & Definitions Chapter 12 Electrostatics

FSc ICS Notes Physics XII Short Questions & Definitions Chapter 12 Electrostatics 2nd Year Physics Notes Online Taleem Ilmi Hub

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Electrostatics: Electricity at rest; electric charges located on insulators.

Electric charge: Quantity of electricity; flow of electrons in a conductor.

Electric current: The rate of flow or charge past a given point in an electric circuit.

Electron: Smallest unit of electric charge.

Proton: An elementary particle with appositive charge (+1.502 C) and rest mass 1.673 x 10(-27) kg.

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

Conductance: Ability to conduct electricity.

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

Electrification: The process of charging a body by adding or removing electrons.

Coulomb: The quantity of electricity transported in one second by a current of one ampere; equal to charge on 6.25 x 10(18) electrons.

Coulomb’s law: The force of attraction or repulsion between two point charges is directly proportional to the product of their magnitudes and inversely proportional to the square of distance  between them.

Point charges: The charged bodies that are very small as compared with the distance between them.

Permittivity (ε): The ratio of the electric displacement in a dielectric medium to the applied electric field strength, i.e. ε = D / E . It indicates the degree to which the medium can resist flow of electric charge. It is measured in farads / meter.

Permittivity of free space (or Electric constant) εo : It is equal to 1 / (c(square) μo ) where c is the speed of light and μo is the permeability of free space.

Relative permittivity (or Dielectric constant) εr :

• The ratio of the capacitance with a particular material separating the plates of a capacitor to the capacitance with a vacuum between the plates.
• It is the ratio of the permittivity of a medium to the permittivity of free space, i.e. ε / εo

Coulomb force: A force of attraction or repulsion resulting from the interaction of the electric fields surrounding two charges particles.

Dielectric (or Dielectric medium): The insulating material between the plates of a capacitor.

Bakelite: A trade name for certain phenol-formaldehyde resins.

Benzene (C6 H6 ): A colourless liquid hydrocarbon. It is now made from gasoline from petroleum. (formerly obtained from coal tar)

Mica: A mineral consisting of complex silicates, characterized by a perfect separating along a line of natural splitting enabling the crystals to be split into very thin plates.

Paraffined paper: Waxy paper oiled with petroleum product.

Plexiglas (Perspex or LUCITE): A tough transparent thermoplastic that is much lighter than glass and does not broken off from a whole.

Teflon: Trade name for a form of polytetrafluoroethene.

Polytetrafluoroethene (PTEE): A material with ‘anti-stick’ properties used for coating cooking utensils and non-lubricated bearings. It’s a thermosetting plastic with a high softening point (327 C) prepared under pressure of 45-50 atmospheres.

Electric field: The region in which an electric force acts on a charge brought into the region.

Electric field intensity(or Electric intensity): The force experience by a unit positive charge placed at that point in an electric field.

Newton’s universal gravitational law (or Law of Universal Gravitation):

• The force of attraction between two objects is directly proportional to the product of their masses and inversely proportional to square of distance between their centers.
• Everybody in the Universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Test charge: A charge placed in the electric field to measure its intensity.

Unit vector: A vector of unit magnitude and points along the required direction.

Density: Amount of charge per unit dimension.

Surface charge density: Amount of charge per unit area.

Volume charge density: Amount of charge per unit volume.

Electric field line (or Electric line of force):

• A line so drawn that a tangent to it at any point indicates the orientation of the electric field at that point.
• The path a free positive charge takes when it is placed in an electric field.

Dimension: A measurement of any sort; especially length, height and width.

One dimension: A measurement which needs a single reference point; e.g. a point on line.

Two dimensions: Measurement needing two references; e.g. a point on a plane (x-y plane).

Three dimensions: Measurement which needs three references; e.g. a point in space (x-y-z coordinate system).

Four dimensions: Measurement which needs four references; e.g. a point in space + time coordinates (relativistic frame of reference).

Radial: Lines or parts extending or proceeding from a centre; acting or moving along lines proceeding from a center; Lines going outwards from a central region.

Zero field spot (or Neutral zone): The middle region between like charges where the electric field intensity is zero.

Tangent: A line, curve, or surface which touches another at a single point.

Static charge: Stationary or motionless charge. An accumulation of static electricity on a body.

Xerography: A photographic process, in which the image is formed by electrical effects rather than chemical effects.

Toner:

• In a document copying machine, image forming material used in electrostatic processes.
• A thermoplastic material impregnated with lampblack. Toner adheres to the exposed areas on the photoconductor during the developing process and is then transferred to the paper to form the developed image on the paper.

Drum: A hollow cylinder around which the photoconductor is wrapped; the drum continuously rotates during printing and carries the photoconductor past the various stations in the printing process. The drum also contains the photoconductor supply and takeup spools.

Selenium (Se): A metalloid element belonging to group VI of the periodic table. It is a semiconductor. There are a number of allotropic forms, including grey, red, and black selenium. The grey allotropic is light-sensitive and is used in photocells, xerography, and similar applications.

Allotropy: The existence of elements in two or more different forms.

Photoconductor: A medium for transferring images to paper.

Silhouette: An object seen as a dark outline against a lighter background; a dark shadow.

Printer: An output unit that produces a hard copy record of data mainly in the form of a sequence of discrete graphic characters that belong to one or more predetermined character sets.

Inkjet printer: A nonimpact printer in which the characters are formed by projecting particles or droplets of ink onto paper.

Gutter:

• A shallow trough fixed in the base, or a channel at the side, to carry off not worth matter
• In multicolumn formatting, the space between columns.

Electrode:

• A conducting element in cell, electronic tube, or semi-conductor device.
• Metal or carbon plates in an electric cell.

Droplet: To fall in a small spherical mass of free liquid.

Electric flux: Electric lines of force in an electric field considered collectively.

Intensity: The electric lines of force transmitted per second through a unit area.

Closed surface: A surface without any end, such as, outer surface of a sphere.

Gauss’s law: The flux through any closed surface is 1/∈o times the charge enclosed by that surface.

Gaussian surface: A closed surface drawn in an electric field.

Equipotential surface: A surface over which the potential has the same value for all points lying on it.

Surface charge density: Amount of charge per unit area.

Volume charge density: Amount of charge per unit volume.

Electric potential: The quantity which determines the flow of electricity.

Electrostatic equilibrium: Such electric field in which a charged particle move with uniform velocity.

Potential: The quantity which determines the flow of electricity.

Electrical potential energy: The energy involved in bringing it to its current state from some reference state.

Electric potential difference: The work done per unit charge as a charge is moved between two plates in an electric field.

Absolute potential: The amount of work done in moving a unit positive charge from infinity to that point against the electrical forces.

Electroencephalograph (EEG): A sensitive instrument that records the voltage waveforms associated with the brain. The trace obtained is known as an electroencephalogram.

Electroencephalogram: The traces of the voltage waveforms associated with the brain taken from electroencephalograph machine.

Electroencephalography: Study of brain waveforms observed by electroencephalograph.

Potential gradient: The change in potential per unit distance.

Radial: Lines or parts extending or proceeding from a centre; acting or moving along lines proceeding from a center; Lines going outwards from a central region.

Infinitesimal: An extremely small or insignificant quantity, amount, etc.

Shark: A member of a large superorder fishes typically having a long streamlined body, many pointed teeth, five to seven slits as the organs of respiration, rough skin consisting of scales.

Ampullae of Lorenzini: Special organs of sharks those are very sensitive to electric field.

Retina: The inner, sensitive coating of the eye containing the ends of the nerves of sight; the part of the eye which receives images of the object.

Iris: The circular coloured membrane of the eye.

Pupil: The opening in the iris of the eye, through which rays of light pass to the retina.

Cornea: The transparent circular outer covering at the front of the eye, over iris and pupil.

Electroretinography (ERG): Electrotretinography is an eye test used to detect abnormal function of the retina. During the test, an electrode is placed on the cornea to measure the electrical responses to light of the cells that sense light in the retina at the back of the eye. These cells are called the rods and cones.

Electron volt: The energy required to move an electron between two points, which have a potential difference of one volt.

Microscope: An optical instrument for producing an enlarged image of small objects.

Gravitational force (or Force of gravitational attraction): The mutual force of attraction which acts universally between two bodies of matter.

Conservative force: A force is conservative if the work done by that force when moving an object from one point to another is independent of the path taken between those two points; e.g. gravitational force.

Electrostatic (or Electromagnetic or Coulomb) force: Force of attraction or repulsion between two un-like or like charged bodies.

Gravitational constant (G): The constant of proportionality in the equation that expresses Newton’s law of universal gravitation: F = G m1 m2 / r(square) . The value of G is 6.67 x 10(-11) N m(2) kg(-2) .

Electric constant (or Permittivity of free space) εo : It is equal to 1 / (c(square) μo ) where c is the speed of light and μo is the permeability of free space.

Atomizer: An instrument for changing a liquid to a very fine spray.

Terminal speed: Maximum constant speed of an object falling vertically downward.

Stokes’ law: In fluid resistance: The drag force F of a sphere of radius r moving with a velocity v through a fluid of infinite extent is F = 6 π η r v where η is the viscosity.

Viscosity: The property of fluids by which they resist their flow due to internal friction.

Coefficient of viscosity: It is equal to the tangential force per unit area required to maintain a unit relative velocity between its two layers, unit distance apart.

Density: Amount of charge per unit dimension.

Capacitor(or Electric condenser): A combination of conducting plates separated by an insulator and used to store an electric charge.

Capacitance:

• The ratio of the charge on either plate of a capacitor to potential difference between the plates.
• Capacity of electric condenser, or capacitor, to store electric charges.

Farad: The Farad is the capacitance of a capacitor between the plates of which there appears a difference of potential of one volt when it is charged by a quantity of electricity equal to one coulomb.

Dielectric: The insulating material between the plates of a capacitor (or condenser).

Relative permittivity ( Dielectric constant or Dielectric coefficient) : The ratio of the capacitance with a particular material separating the plates of a capacitor to the capacitance with a vacuum between the plates.

Voltmeter: A meter used for measuring potential differences.

Electric polarization: The separation of the charges in the molecules of an insulator as an effect of an electric field. One face of an insulator in a field gains a net positive charge with the other becoming negative.

Dipole: A system of two equal and opposite charges placed at a very short distance apart.

Dipole aerial: TV receiving antenna, cut to one-half wavelength of the transmitted signal.

Resistance: The opposition to the flow of electricity.

Resistor: A component included in the electric circuit because of its resistance.

Time constant: Time required by capacitor to deposit 0.63 times equilibrium charge qo . Physical quantities such as voltage, current and temperature sometimes decrease with time in such a manner that, at any instant, the rate of decrease of the quantity is given by: - (dν / dt) = ν / T where ν is the instantaneous value of the quantity, T is time constant.

Written By: Asad Hussain