Basic Circuit Elements- Resistance

Different types of Resistance
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It is defined as the property of a substance due to which it opposes the flow of current (i.e. electrons) through it resistance is denoted by capital letter  R  and its symbol is

Resistance Symbol

Resistance is one of the basic element of an electric circuit . The  practical resistance is called a resistor and its unit is "ohm" () .A conductor is said to have a resistance of one ohm if it permits one ampere current to flow through it when one volt is applied across its terminals.

Metals , acids and salts are good conductor of electricity due to presence of a large number of free or loosely  attached -electrons in their atoms. Hence they have a very large resistance. Resistance is a passive element and hence dissipates power in the form of heat. The power dissipated by a resistance can be given as
P = vi

                          =ⁱ/_Ri       OR   ^v/_Rv

Laws of Resistance :-

The resistance R offered by a conductor depends on the following factors :

1. It varies directly as  length l of conductor.
2. It varies inversely as the cross sectional area A of the conductor. 
3. On the nature of material.
4. On the temperature of the conductor.

R ?^l/_A

R = ?^l/_A

where P is proportionality constant or specific resistance or resistivity.