Electrostatics (3 Mark Definitions)

Frage	Antworten
Applications of Attraction and Repulsion	a) Electrostatic paint spraying b) Powder coating c) Fly-ash collection (chimneys) d) Ink-jet printing e) Photostat copying (Xerox)
Quantization of Electric Charge	Electric charge of any system is always an integral multiple of the least amount of charge. The quantity can take only one of a discrete set of values.
Conservation of Electric Charge	Electric charge can neither be created nor destroyed. Total charge of an isolated system always remains constant, but charges can be transferred from one part of the system to another. 92 U 238 --> 90 Th 234 + 2 He 4
Coulomb's Law	The force of attraction or repulsion between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. The direction of the forces is along the line joining the two point charges.
Coulomb	One coulomb is defined as that quantity of charge, which, when placed at a distance of 1 m in air/vacuum from an equal and similar charge, experiences a repulsive force of 9 x 10^9 N.
Electric Field Intensity	Electric field intensity at a point in an electric field is defined as the force experienced by a unit positive charge kept at that point. It is a vector quantity. Its unit is N C^-1
Electric Line of Force	An imaginary straight or curved path along which a unit positive charge tends to move in an electric field.
Electric Dipole	Two equal and opposite charges separated by a very small distance. Ex: Water, ammonia, carbon dioxide, chloroform
Electric Dipole Moment	The dipole moment is given by the product of the charges and the distance between them. Diploe moment, p = q2d (or) 2qd
Electric Potential Energy	Electric potential energy of an electric dipole in an electrostatic field is the work done in rotating the dipole to the desired position in the field.
Microwave Oven (Principle)	a) Microwaves produce a non-uniform oscillating electric field. b) Water molecules are electric dipoles (excited by an oscillating torque) c) Bond breakage releases energy used to cook food.
Potential Difference	Potential difference between two points in an electric field is defined as the amount of work done in moving a unit positive charge from one point to the other against the electric force.
Volt	The unit of potential difference. Potential difference between two points is 1 volt if 1 joule of work is done in moving 1 coulomb of charge from one point to another against the electric force.
Electric Potential at a Point	The amount of work done in moving a unit positive charge from infinity to that point against the electric forces.
Electric Potential Energy (Two Point Charges)	a) The work done to assemble two charges b) The work done in bringing each charge c) Work done in bringing a charge from infinite distance.
Equipotential Surface	A surface on which all the points are at the same electric potential.
Electric Flux	The total number of electric lines of force crossing through the given area. It is a scalar quantity. Its unit is N m^2 C^-1
Gauss' Law	Total flux of the electric field over any closed surface is equal to 1/ε◦ times the net charge enclosed by the surface (Gaussian surface).
Electrostatic Shielding	The process of isolating a certain region of space from external field. It is based on the fact that the electric field inside a conductor is zero.
Bus vs. Open Ground	During thunder accompanied by lightning, it is safer to sit inside a bus than in open ground/under a tree. The metal body of the bus provides electrostatic shielding where the electric field is zero. During lightning, the electric discharge passes through the body of the bus.
Electrostatic Induction	It is possible to obtain charges without any contact with another charge. They are known as induced charges and the phenomenon of producing induced charges is called electrostatic induction.
Capacitor	A charge storage device consisting of one or more pairs of conductors separated by an insulator.
Capacitance	The ratio of charge given to a conductor to the potential developed in it. Its unit is farad. A conductor has a capacitance of 1 farad if a charge of 1 coulomb given to it raises its potential by 1 volt.
Dielectric	An insulating material in which all the electrons are tightly bound to the nucleus. There are no free electrons to carry current. The electrons are not free to move under the influence of an external field.
Non-Polar Molecule	A molecule in which the center of gravity of the positive charges (protons) coincides with the center of gravity of the negative charges (electrons). Eg: Oxygen, nitrogen, hydrogen
Characteristics of Non-Polar Molecules	a) No permanent dipole moment b) Centre of charges gets displaced in an electric field c) Such molecules are polarized and are called induced dipoles. d) They acquire dipole moment in the field direction.
Polar Molecule	A molecule in which the center of gravity of the positive charges is separated from the center of gravity of the negative charges by a finite distance. Eg: Nitrous oxide, water, hydrochloric acid, ammonia
Characteristics of Polar Molecules	a) Permanent dipole moment. b) Dipole moments orient the molecules in random directions in the absence of an external field (no net dipole moment). c) Dipoles orient themselves in the direction of the electric field on its application.
Polarization	Alignment of dipole moments of polar molecules of the permanent/induced dipoles in the direction of the applied electric field.
Applications of Capacitors	a) Ignition systems of automobile engines (elimination of sparking). b) Voltage fluctuation reduction in power supplies (power transmission efficiency increased). c) Generation of electromagnetic oscillations and radio circuit tuning.
Capacitors in Series	The reciprocal of the effective capacitance is equal to the sum of the reciprocals of the individual capacitances.
Capacitors in Parallel	The effective capacitance is the sum of the capacitances of the individual capacitors.
Corona Discharge / Action of Points	The leakage of electric charges from the sharp points on the conductor.

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