ELECTROSTATICS

Coulomb’s law: The force between two charges q₁ and q₂ separated by distance r in vacuum is

F=  =    where  is the permittivity of free space.

K =  = 9x10⁹ Nm²/C²

 = 8.85 x 10^-12 C²/Nm²

 

Electric Field intensity at a distance r from a point charge q is

E =  =

 

Electric Potential at a distance r from a charge q is

V =  =

 

Electric Field intensity at a distance r from to a thin infinitely long wire of uniform linear charge density  is

E =

 

Electric Field intensity due to an infinitely thin plane sheet of uniform surface charge density  is

 

E =

 

 

Electric Field intensity at a distance r from the centre of a thin spherical shell of radius R and charge q is

E =, r  R

E    = 0          r  R

 

 

                                                      CURRENT ELECTRICITY

Current (I) is the charge (Q) flowing per unit time (t)

I = Q/t

 

Ohm’s Law: The current (I) flowing through a conductor is directly proportional to the potential difference (V) across the ends of the conductor, provided the physical conditions remain constant.

 

V = I R, where R is the resistance of the conductor

 

Equivalent Resistance (R_eq) of Resistors in Series is

R_eq = R₁ + R₂ + R₃ + - - -

Equivalent Resistance (R_eq) of Resistors in Parallel is given by

1/R_eq = 1/R₁ + 1/R₂ + 1/R₃ + - - -

Electric Power is the rate of dissipation of electric energy in an electric device.

P = VI = I²R = V²/R

Electrical energy consumed in a circuit in time‘t’ is

U = VIt = I²Rt = V² t/R