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What is electron drift velocity ?

Electron Drift Velocity : Suppose that in a conductor, the number of free electrons available per m3 of the conductor material is n and let their axial drift velocity be ν metres/second. In time dt, distance travelled would be ν × dt. If A is area of cross-section of the conductor, then the volume is νAdt and the number of electrons contained in this volume is νA dt. Obviously, all these electrons will cross the conductor cross-section in time dt. If e is the charge of each electron, then total charge which crosses the section in time dt is dq = nAeν dt. Since current is the the rate of flow of charge, it is given as
i = dq nAe dt
dt dt ν = ∴ i = nAeν

What is Resistance?

It may be defined as the property of a substance due to which it opposes (or restricts) the flow of electricity (i.e., electrons) through it.

It is due to the presence of a large number of free or loosely-attached 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 electrons, thereby producing heat.

The practical unit of resistance is ohm. The symbol for ohm is Ω.

what are the Laws of Resistance?

The resistance R offered by a conductor depends on the following factors :
(i) It varies directly as its length, l.
(ii) It varies inversely as the cross-section A of the conductor.
(iii) It depends on the nature of the material.
(iv) It also depends on the temperature of the conductor.

What is the unit of resistivity?

the unit of resistivity is ohm-metre (Ω-m).

what are conductance and conductivity?

Conductance (G) is reciprocal of resistance. Whereas resistance of a conductor measures the
opposition which it offers to the flow of current, the conductance measures the inducement which it
offers to its flow.
where σ is called the conductivity or specific conductance of a conductor. The unit of conductance
is siemens (S). Earlier, this unit was called mho.

the unit of conductivity is siemens/metre (S/m).

What is ohm’s Law?

This law applies to electric to electric conduction through good conductors and may be stated as follows :
The ratio of potential difference (V) between any two points on a conductor to the current (I) flowing between them, is constant, provided the temperature of the conductor does not change. In another way, it simply means that provided R is kept constant, current is directly proportional
to the potential difference across the ends of a conductor.

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