Sunday, April 12, 2009

2. Electrostatic

Previous sections:
1. Introduction

2. Electrostatic

In this chapter, we will only concern ourselves with electrostatic, which means that there is no rate of change of electric charges with respect to time (In other words, as time passes by, the quantity of electric charges remain the same. Another way to look at this is to say that it is in equilibrium). This definition is important and the reader should always be careful that this criteria is met when applying theories and equations from this chapter.

It is also important know our objective of this chapter. What do we expect to know at the end of this chapter? We expect this:

∇.D=ρ and ∇xE=0

which are the two fundamental equations in electrostatic.

Looks simple enough! At the end of this chapter, I hope the reader would have understood how these equations are formulated and what do they mean physically.

We will begin by seeing how the investigation of force acting on electric charges (in vacuum space) leads to electric field and Coulomb's Law. Applying Gauss's Law, we shall see how does this gives rise to the first of the two fundamental equations of electrostatic, i.e.


Next, we will see how we need to modify the equations to account for dielectric materials, which give rise to the quantity, ε_r, called relative permittivity.

Finally, we look at the experiments concerning current-carrying conductors, which will give us the second equation for electrostatic, i.e.


This is all there is to electrostatic! The rest are just clever mathematical tricks performed on the equations to solve complex problems.

1 comment:

shinliang said...

i made some changes to this entry.
instead of saying electrostatic means no rate of change of electric field AND no magnetic field, i chose to say now that electrostatic CAN have magnetic field, as in the case of steady current.

in the case of steady current, magnetic fields exist, but electrical charges are still in equilibrium and fields are static