# RE: Physics of Wireless Transmission (Units)

```Original poster: "Godfrey Loudner" <ggreen@xxxxxxxx>

Hello Dave

The expression you refer to is I/(2 Pi epsilon c^2 R) where I is
current, epsilon is the permittivity of free space, c is the of the
speed of light, and R is distance. In the MKS system of units, I is
Ampere, epsilon is Coulomb^2/(Newton meter^2), c is meter/sec, and R is
meter. Now the dimension of (epsilon c^2 R) is (C^2/(N m^2))(m^2/s^2)m =
C^2 m/(N s^2). So the dimension of the expression is A N s^2/(C^2 m) =
(C/s)N s^2/(C^2 m) = s N/(C m) = N/[(C/s) m]
= N/(A m)= Tesla. Tesla is the unit for the magnetic field B. So there
is nothing wrong with the expression in the sense of units. BTW thanks
for an article that makes really good reading. I think there's enough

Godfrey Loudner

Hi Terry, Bob, and all,

I have found a web page that presents the mathematics behind
relativistic charge: http://physics.weber.edu/schroeder/mrr/MRRtalk.html

You will note in equation 3 it says, "The expression in parentheses must
be the magnetic field strength."  When you work out the actual
dimensions for the term in the parentheses, you get mass per time, which
is not the unit of magnetic field strength.

Dave

```