electrostatics

Electric field

E=F/q or E=\frac{q}{4\pi\varepsilon_0r^2}r ← outside r is a vector between charges

Coulomb’s law

F=\frac{qQ}{4\pi\varepsilon_0r^2} (on formula sheet)

Electric flux

\phi=EA\cos\theta

Or

\phi=\int_{S}^{.}E\cdot dA=\frac{\sum q}{\varepsilon_0} (in formula book)

Gauss’ law

The total electric flux out of a closed surface is proportional to the net charge enclosed

\phi=\frac{Q}{\varepsilon_0}

Electric field for point charge

E=\frac{q}{4\pi\varepsilon_0r^2}

Electric field for a charged plate/ sheet of charge

E=\frac{\sigma}{2\varepsilon_0}

\sigma is surface charge density

Electric potential/ potential difference

In formula book

Electric potential is gauss’ law is not suitable

Sum then together

Potential for electric dipole

V=\frac{qd\cos\theta}{4\pi\varepsilon_0r^2}

Isolated conductors

• electric field everywhere inside must be zero

• electric field outside is perpendicular to the surface

• any net charge must lie at the surface