Full Information about Resistance

Definition of RESISTANCE:

It is the property of the material by virtue of which it oppose the flow of electric current.

The Electrical Resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. in other word it is The inverse quantity is electrical conductance.

Metal, Acid and salt solutions are good conductors of electricity.  Pure Metals like Silver, Copper, Aluminium, Gold are very good conductors.

non metals like Bakelite, mica, glass, PVC, rubber,dry wood are poor conductor of electricity.

UNIT OF RESISTANCE:

Practical Unit of resistance is ohm ( as scientist George Simon Ohm discover this ). a conductor is said to have a resistance of 1 ohm if it permit 1 ampere current flow through it when 1 volt potential difference impressed across its terminal. symbol of ohm is- Ω, Symbol of resistance is- R

there are many bigger and lower quantity of resistance there units are given bellow:

Mega-ohm (MΩ)- 1000000ohm

Kilo-ohm(KΩ)- 1000ohm

Mili-ohm(mΩ)- 0.001ohm

Micro-ohm(μΩ)- 0.000001ohm

LAW OF RESISTANCE:

The resistance(R) offered by a conductor depends on the following factor:

• It Varies directly as its Length (L).
• it varies inversely as the cross-section area (A) of the conductor.
• its depends on the nature of the materials.
• its depends on the temperature of the conductor or  atmosphere.

R∝L/A

EFFECT ON TEMPERATURE ON RESISTANCE:

There are two type of resistance:

1. Positive Temperature coefficient- Varies directly as its temperature.(EX- metals)
2. Negative Temperature coefficient- Varies Inversely as its temperature. (Ex- Non Metals and Semi conductors, Carbon is a good Example of this)

Type of Resistor: 

there are many types of resistor available there are- carbon composition,deposited carbon,high-voltage ink film, metal film, metal glaze, wire-wound, cermet (ceramic Metal).

Linear Resistance:

those element whose V-I curves are straight lines are called linear element as their resistance are linear. ex- carbon resistance, metals.

Non-Linear Resistance:

those elements whose V-I curves are not straight line are called non-linear element as their resistance is non-linear.  ex- diodes, lamps, thermistors,  varistor.

OHM's Law:

The ratio of potential difference (V) between any two points on a conductor to the current (I) flowing between them is constant (temperature of the conductor does not change)

V/I=constant     [ here constant is R (Resistance)

OHMIC and NON OHMIC Resistance:

OHMIC- Those resistance which Follow Ohm's Law (V=IR).

NON-OHMIC- Those which not follow Ohm's Law(V=IR).

There are two type of combination of resistance uses in electrical and electronics-

Series Combination:- when conductor having Resistance R1, R2, R3, are joined end -on-end they are said to Series Connected.

Parallel Combination:- Resistors are said to be connected together in “Parallel” when both of their terminals are respectively connected to each terminal of the other resistor or resistors.

what is a Fuse?  Fuse wire