Simple Note For Lecture Class

Electric current      

i = dq/dt

Current density       

J = i/A        (A/m²)

      Drift speed           

J = (ne)v_d

Resistance             

R = V/I    , R = ρL / A

         

Resistivity             

ρ = E/J

Conductivity           

σ = 1/ρ

Ohm’s law

A given device (conductor, resistor, or any other electrical device) obeys Ohm’s law if its resistance R, as V/i, is independent of the applied potential difference V. A given material obeys Ohm’s law if its resistivity, is independent of the magnitude and direction of the applied electric field E.

A Microscopic View of Ohm’s Law

resistivity of metal , ρ = m / e2nT

Power in Electric Circuits

       P = IV = I²R = V²/R

Semiconductors are materials that have few conduction electrons but can become conductors when they are doped with other atoms that contribute free electrons.

Superconductors are materials that lose all electrical resistance at low temperatures. Recent research has discovered materials that are superconducting at surprisingly high temperatures.


written by SHAIRAH :)