Electric Field Lines
Electric Field Lines
The rules for drawing electric field lines are as follows: 
•The lines must begin on a positive charge and terminate on a negative charge. In the case of an excess of one type of charge, some lines will begin or end infinitely far away.
•The number of lines drawn leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge.
•No two field lines can cross.
Electric Field Lines
Motion of Charged Particles in a Uniform
Electric Field
(11.12)
(11.13)
Motion of Charged Particles in a Uniform The Cathode Ray TubeElectric Field
Electric Flux
The product of the magnitude of the electric field E and surface area A perpendicular to the field is called the electric flux ΦE 
(11.14)
From the SI units of E and A, we see that ΦE has units of newton-
meters squared per coulomb (N·m2/C.) Electric flux is proportional to the number of electric field lines penetrating some surface.
Electric Flux
(11.15)
Electric Flux
(11.16)
Electric Flux
The net flux through the surface is proportional to the net number of lines leaving the surface, where the net number means the number leaving the surface minus the number entering the surface.
(11.17)
Electric Flux
Ex. Flux Through a Cube
The net flux through faces 1 and 2 is
The net flux through faces 3 and 4 is zero.