Important Formulae I

1) F = qE

• where F is Force,
• q is Charge, and
• E is Electric Field.

2)  Coulomb's Law


According to this law, two stationary point-charges q1 and q2 repel or attract each other with a force F which is directly proportional to the product of the charges and inversely proportional to the square of the distance r between them,
When the charges are placed in vacuum (or air), then we write

where 1/(4πε_o) is a (dimentional) proportionality constant which depends on the units used for charges, distance and force. The force F acts along the line joining the charges and the force on q₁ is equal to that on q₂. Coulomb's Law holds for 'point-charges' only and is valid only for static charges (i.e., charges that are not moving).

3) Electric Field

The force experienced by a net charge when placed in an electric field.

4) Electric Flux

Electric Flux is a measure of number of lines of force passing through some surface held in the electric field.

4) Gauss Theorem

It states that the total flux to any closed surface is equal to 1/ε_{o times the total charge.}

5) Torque on a Diapole