Electric fields, Superposition, Motion of charged particles in uniform electric field

This lecture is based on Serway, Sections 23.4 - 23.7.

One can represent the electric field by means of arrows, or by means of continuous lines
- lines originate on positive charges
- lines terminate on negative charges
- lines never cross
- the density of lines indicates the strength of the electric field
The principle of superposition states that the electric field due to a group of particles is simply the vector sum of the electric field due to each particle considered individually
The electric field of a dipole decreases with distance cubed (not squared)
One can calculate the electric field due to a continous distribution of charge by integrating the contributions of each little bit of material
When calculating electric fields,
- look for symmetry -- it can eliminate one component of the field
- figure out what the appropriate charge density is
- divide the object into little chunks
- figure out the charge density of each chunk (it may depend on position)
- calculate the electric field created by each chunk
- set up the integral, then integrate
- check the sign of the answer when finished
- look at the behavior of the field in limiting cases (e.g. very far away); do they make sense?
a charged particle in a uniform electric field experiences a constant acceleration -- like an object falling in a uniform gravitational field
it obeys the same 1-D kinematic equations you learned in mechanics

This is an example of calculating the electric field due to a disk with varying charge; it's complicated, but shows the same steps as the problems we did in class.
Appendix problem, viewgraph 1
Appendix problem, viewgraph 2
Appendix problem, viewgraph 3
Appendix problem, viewgraph 4
Appendix problem, viewgraph 5