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MHT-CET : Physics Entrance Exam

MHT - CET : Physics - Current Electricity Glossary

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         Electric Current: The electric current is the rate of flow of charge.

I=

Q

t

          

         Current Density: It is a microscopic quantity related to the current. It is given by

J =

iA,

where J =

Current density

i =

Current through an infinitesimal area A

A =

An infinitesimal area in a conductor normal to the flow of current.

          

         Drift Velocity: When a current flows through a conductor, free electrons in the conductor have a velocity in the direction of the positive potential superimposed over their random motion. Thus, they drift with a drift velocity vd in a direction opposite to the applied electric field.

         e. m. f.: The e.m.f. of a cell is the amount of work done by the cell in sending a unit positive charge around a complete circuit.

         Ohm's Law: If physical conditions remain constant, the current flowing through a conductor is directly proportional to the potential difference applied across it.

         Local Action in a Voltaic Cell: Zinc rod contains several impurities such as carbon, iron, lead, etc. These form a number of miniature cells on the zinc rod and produce local currents. This local action causes unnecessary consumption of zinc.

         Polarisation in a Voltaic Cell: A non-conducting layer of hydrogen gas accumulates on the copper plate of a cell and sets up back e.m.f. This obstructs the flow of positive hydrogen ions towards the copper plate. This phenomenon is known as polarisation.

         Kirchhoff's First Law (KCL): The algebraic sum of all currents at a junction of a node is zero. (SI = 0 at a junction).

         Kirchhoff's Second Law (KVL): The algebraic sum of all the potential differences and the e.m.f.s in a closed loop is zero. (SIR + E= 0).

         A Balanced Wheatstone's Network: When the values of four resistances in Wheatstone's network are so adjusted that the current flowing through the galvanometer in a Wheatstone's network is zero, the bridge is said to be balanced.

Balancing condition

P

Q

=

R

S

          

         Potentiometer: It is used to measure e.m.f. and internal resistance of a cell. It measures e.m.f.s more accurately than a voltmeter

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