Current Electricity

Electric Current and Drift of Electrons

  • The time rate of flow of charge through any cross section is called current i = q/t.
  • Current is having direction but it is scalar.
  • The conventional direction of current is taken to be the direction of flow of positive charge.
  • If "n" particles each having a charge 'q' pass through a given area in time 't'. \tt i = \frac{nq}{t}
  • If a point charge "q" is moving in a circle of radius "r" with speed "v" then. \tt i = \frac{qv}{2 \pi r}
  • Drift velocity (vd) is the average velocity acquired by force electrons inside a metal by electric field.
  • Drift velocity depends up on electric field.
  • Drift velocity decreases with increase of temperature.
  • The mobility of a charge is the average drift velocity resulting from the application of unit electric field. \tt \mu = \frac{Vd}{E}
  • Mobility of charge carries can be experimentally determined by Hall effect.
  • Current density (j) is the amount of charge flowing per unit cross-sectional area per second. \tt J = \frac{i}{A}
  • The direction of current density is the flow of positive charge
  • Relation between electric current and drift velocity i = neAvd.
  • Relation between current density and drift velocity J = ne vd.
  • The property that opposes the flow of current through it is called electric Resistance. (R). \tt R = \frac{V}{i}
  • Unit of resistance is ohm.
  • Resistance depends up on length and area of cross section. Nature of materials and temperature.

View the Topic in this video From 06:31 To 58:00

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1. Free electron density in a metal is given by n = \frac{N_{A}x d}{A} where NA = Avogadro's number, x = number of free electrons per atom, d = density of metal and A = Atomic weight of metal.

 2. Electric Current (I)
The rate of flow of charge through any cross-section of a wire is called electric current flowing through it.
Electric current (I) = \frac{q}{t}.

3. Drift Velocity of Free Electrons
When a potential difference is applied across the ends of a conductor, the free electrons in it move with an average velocity opposite to the direction of electric field, which is called drift velocity of free electrons.
Drift velocity v_{d} = \frac{eE \tau}{m} = \frac{eV \tau}{ml}

4. Current Density
The electric current flowing per unit area of cross-section of a conductor is called current density.
Current density (J) = \frac{I}{A} = nev_{d}

5. Mobility
The drify velocity of electron per unit electric field applied is called mobility of electron.
Mobility of electron (\mu) = \frac{v_{d}}{E}