Re: Re:Electrostatics (was Charge distribution on a Toroid (was spheres vs toroids)0

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Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi Robert,

 > Original poster: "Robert Jones" <alwynj48-at-earthlink-dot-net>
 >
 > The charge thread got me thinking about electrostatics. I realized I was
 > very rusty on the subject. I tried to recap the fundamentals but found a
 > problem with my thinking.
 >
 > Can someone explain were I have gone wrong. It may help others too.
 >
 > 1. Charge is the fundamental quantity and can be positive and negative
 >
 > 2. Like charges repel and opposite charges attract with a force
proportional
 > to the product of the charges and inversely proportional to square of the
 > distance.
 >
 > 3. Voltage is a measure of the energy required to move a charge from one
 > location to an other i.e. if there are charges there already the moving
 > charge will experience a force, force x distance is energy.
 >
 > 4. Lines of flux are the direction of the energy required with respect to
 > space for 3.

Not to be confused with magnetic flux (closed lines).  Electric flux are
open ended and are in the direction of the electric field.  The movement of
a test charge between two points of differing voltages does not necessaryly
need to take the path of the E field, hence the dot product  E.dl

 > 5. The energy required to move a charge is a property of the material
 > surrounding the location that the charge will reside at. This is usually
 > referred to as energy stored in the surrounding medium as electrostatic
 > strain i.e. energy in the field. The permittivity thing.
 >
 > The above seems to be right. However due to 2 the force is only a function
 > of the charge on an object where as 3 and 5 suggest it's also a function
of
 > the capacitance???
 >
 > Were have I gone wrong?  Yes I know the above are not rigorous definitions
 > but I think they will do.
 >
 > Bob

I think all your statements 1-5 are OK.  Statement 2 is correct as far as it
goes, there are proportionality constants not stated in #2

F = q1q2/(4pi*permittivity * r^2)

Gerry R
Ft. Collins, CO