In this topic, you study the definition, unit and formula of Resistance. And also factors on which the resistance depends.
It is the property of the substance. It is defined as the property of the material by virtue of which it opposes the flow of current through it. The unit of resistance is Ohm (Ω). It is measured by Ohm meter directly. It is represented by the letter R.
One ohm: It is the resistance offered by a substance when one volt of electric pressure results one ampere current through it. The other units are as
- one megohm = 106 Ohm
- one microohm = 10-6 Ohm
- one milliohm = 10-3 Ohm
- one kilo ohm = 103 Ohm
International Ohm
It is the resistance offered by a conductor of mercury column at the melting ice temperature, 14.4521 gm in weight, having 106.3 cm length and a uniform cross-sectional area of 1 mm2.
Conductance
It is the reciprocal of resistance. It is the property of a substance by virtue of which it helps in the flow of current. It is measured by Ohm meter. The unit is mho and denoted by letter G.
On what factors does the resistance of a conductor depend
There are the following factors upon which the resistance of conductor depends:
Length: The resistance of a conductor depends upon its length. The resistance is directly proportional to the length of the conductor, i.e.,
Area of cross section: The resistance of the conductor is inversely proportional to the area of cross section of the conductor i.e.,
Specific resistance: The resistance also depends upon the nature of the material. The resistance of a conductor is directly proportional to the specific resistance of the material i.e.,
Temperature: The resistance of a conductor also depends upon the temperature, for example the resistance of pure metal increases with the increasing of the temperature.
Mathematically it can be expressed as
where
R =Resistance of the conductor in ohm
p = Specific resistance in Q m
l = Length Of the conductor in m
a =Area Of cross-section in m2
so the resistance of a conductor
Specific resistance x Length
Area of cross-section