MadSci Network: Physics Query:

### Subject: VRD - coulombs, physical constants

Date: Tue Oct 26 11:12:07 1999
Posted by Phil M.
Grade level: School: No school entered.
City: No city entered. State/Province: Queensland Country: AU
Area of science: Physics
ID: 940950727.Ph
Message:
```
BACKGROUND   My problem involves physical constants where :
h = Plancks constant
c =  speed of light
m = mass of an electron
e = electrostatic charge
a =fine structure  constant
p = pi and
r =2.817 X 10^-15 metres and is the dimension (in metres) formerly
associated with the radius of an electron, but can otherwise be thought of
as  the orbital radius of an electron were it able to travel at the speed
of light around a proton.

OBSERVATION   It can be written that :   (e^2 x 10^-7)
= (r m) = ha/2face=Symbol>pc    (kg m)   Please note that the dimension of
kg m (kilograms multiplied by metres)  appears to be equivalent to e^2 X
10^-7 (coulombs squared multiplied by a  dimensionless number).    Also
note that it becomes possible to describe for example electron mass in
terms of coulombs^2 per metre.

QUESTIONS   - the dimensionless number 10^-7 crops up time and again in
electrostatic  equations. Why? What is its
significance? and,   - are coulombs (the unit of electrostatic
charge) interchangeable  with the dimension of the kilogram metre (which
also seems to be a unit of  electrostatic charge)?

```

Re: VRD - coulombs, physical constants

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