Short Notes on Electro Statics

Short Notes on Electro Statics

Number of electrons =(Total charge)/(Charge of one electron)

n=q/e

    

q=ne

 Coulomb’s Law

“It states that two point charges repel or attract each other with a force which is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of distance between them.”

F=1/4Πεο×q1q2/r²

Linear charge density:- λ=q/L     Surface charge density:- σ=q/A Volume charge density:-   ρ=q/V

In Coulomb’s law the charges if placed in another medium,

Then,

F medium = F air / K = 1/4Πεο×1/K×q1q2/r²

Where K is called dielectric constant of medium

E=F/q       

F=qE

Electric field due to a point charge

Consider a single point charge ‘q’ , Let ‘r’ be the vector from q to a general point P where the test charge qο is placed.

By Coulomb’s law,

F=(1/4Πεο)x(qqο/r²)x r^

E=q/qο E=(1/4Πεο)x(q/r²)x r^

The electric field vector points radially outwards if q > 0 and radially inwards if q < 0.

Electric field inside a conductor is zero.

Dipole moment

→           →  P  = q(2a)

Electric field on the axial line of an electric dipole

E=[1/4Πεο]×[(2Pr )/(r²-a²)²] E=[1/4Πεο]×[(4qra )/(r²-a²)²]

When a<<r

Then ,

E=[1/4Πεο]×[2P/r³]

Electric field on equatorial line

E=[1/4Πεο]×[P/(r²+a²)^3/2]

When a<<r

Then ,

E=[1/4Πεο]×[P/r³]

Torque of the dipole in the uniform electric field,

→      →      ζ=P × E

Electric Flux

φ=∫E.ds