1. Unit 1 Day 10 Electric Flux & Gauss’s Law
Definition of Electric Flux
Electric Flux thru a Closed Surface
Gauss’s Law
Derivation of Gauss’s Law from Coulomb’s Law

2. Karl Friedrich Gauss 1777-1855 Developed a generalized and
more elegant relationship
between charge and the
electric field (Coulomb’s Law)

3. Electric Flux
The electric flux refers to the electric field lines that penetrate a given surface
For a given uniform electric field E passing thru an area A, the electric flux is defined as:

4. Electric Flux
θ is the angle between the E-Field and the line drawn normal to the surface
The electric flux thru an area is proportional to the number of E-Field Lines passing thru the area

5. Electric Flux Thru a Closed Surface
In general, an electric field
is not uniform and the area
is not flat !
Any area can be divided up
into n number of small elements
of surface area ΔA, sufficiently small to be
considered flat and the E-field is rather
invariant over this small area. Then:

6. Electric Flux Thru a Closed Surface
In the limit as the sum becomes an integral
Then a surface of any shape that completely encloses a volume of space is given by

7. Electric Flux Thru a Closed Surface
A (+) flux leaving the volume
A (-) flux entering the volume
If every field line that enters a volume exits the volume, then: ; there
is no net flux into or out of the closed surface
The net flux will be non-zero only if the surface encloses a net charge
The value of depends on the charge enclosed by the surface. This is Gauss’s Law !