Unit of Conductivity – Class 11 | Chapter – 2 | Physics Short Notes Series PDF for NEET & JEE
Unit of Conductivity: The unit of electrical conductivity is siemens per meter (S/m) in the SI (International System of Units) system. In the past, the unit of conductivity was often expressed in terms of its reciprocal, electrical resistivity, which is measured in ohm-meters (Ω·m). However, in modern practice, conductivity is the preferred measure and is commonly used to describe the ability of a material to conduct an electrical current.
Unit of Conductivity
The opposite of electrical conductivity is electrical resistance. It is the estimation of the potential of the material to restrict the flow of current. The resistivity of a conductor depends on the area of the material, the nature of the material, and the length of the conductor.
Ωm is the SI unit of electrical resistivity.
Relativity of Different Materials
| Material | Resistivity | |
|---|---|---|
| Conductor | silver
Copper Aluminium Tungsten iron Lead Mercury |
1.59 x 10-8
1.68 x 10-8 2.65 x 10-8 5.6 x 10-8 9.71 x 10 -8 22 x 10-8 98 x 10-8 |
| Alloys | Constantan (cu+Ni)
Manganin (Cu + Ni + Mn) Nichrome (Ni + Cr + Mn + Fe) |
49 x 10-8
48.2 x 10-8 100 x 10-8 |
| Insulators | Glass
Hard Rubber |
1 – 10000 x 109
1-100 x 1013 |
Electrical Resistors
Resistors are used to manage the flow of current in the circuit. It consists of several color codes. The different value of resistance is expressed by the different colors marked on the resistor.
Formula
- When materials have current density and a magnetic field,
ρ = E/J
Where, ρ = the resistivity of the material
E = the intensity of the magnetic field
J = the intensity of the current density
- Conductors with a regular cross-section and a regular flow of electric current. ,
Resistivity (ρ) = R A/l
R = electrical resistance of the regular cross-section
A = area of the cross-section
L = the length of the piece
V = W/Q
Where V = potential difference between two points in an electric circuit
W= work done
Q= charge
P = VI
Where,
P= electric power or the rate at which energy is consumed in the electric circuit
V= potential difference
I= current
- Joule’s law of heating
H= I2Rt
- Ohm’s law
V=IR
Where R = Resistance which is constant at a given temperature
- The relationship between electrical resistivity and electrical conductivity is expressed as
σ = 1/ρ
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