PX157 - B4a - electric flux

introduction

flux is the measure of 'flow' of $\vec{E}$ though a surface
unit: $V m$
consider a closed surface and move a test charge, $q_{0}$ , in its vicinity. measuring the force felt by the charge, the $\vec{E}$ can be measured as:

\vec{E} = \frac{\vec{F}}{q_{0}}

direction of $\vec{E}$	charge inside volume	direction of electric flux
outwards	positive	outwards
inwards	negative	inwards

electric flux from a uniform surface

for a uniform $\vec{E}$ across a flat surface of area $S$ :

ϕ_{E} = \vec{E} \cdot \vec{S}

where, $\vec{S}$ is a vector perpendicular to the surface, $| \vec{S} | = a r e a_{s u r f a c e}$ , and $\vec{E}$ is evaluated on the surface and uniform across the surface