Resistnace
Is is the peoperty of substnace by virtue of which it opposes the flow of electrons(electricity) through it. Metals,acid and salt solutions are good conductors of electricity. Amongst metals Silver, Copper and Aluminium ae very good conductors of electricity. this is due to presence of a large number of free or loosely -atttached electrons in their atoms. These Vagrant electrons assume a directed motion on the application of an electric potential difference. These electrons while flowing pass through the molecules or the atoms of the conductor, collide and other atoms and electons, thereby producing heat.
Those substance which offer relatively greater diffculty or hindrance to the passage of these electrons are said to be poor conductors of electricity like bakelite, mica dry wood etc.They are also called as insulators
Unit
The practical unit of resistance is ohm. A conduator is said to have a resistance of one ohm if it permitsone ampere current to flow through it when one volt is imptressed across its terminals.
