|
Beware of the bull Praise of Academics The
New Scholasticism Throwing glasses at stone houses Portrait of a Drivelmaster… A one-electron man. Can’t handle a whole row of them.Sir Michael Pepper Win a five hundred pound prize UNIVERSITY OF CAMBRIDGE Ivor
Catt, Esq., Dear
Mr Catt, As
a Trinity physicist the Master suggested that I might provide some comments
on the questions raised in your recent letter to him on aspects of
electromagnetic theory. If
I understand the position correctly, your question concerns the source of the
charge at a metal surface which by responding to the presence of the EM wave
ensures that the reflectivity of the metal surface is virtually unity, hence
providing waveguide action and related applications. If I may restate the basis of your question, what is the maximum frequency of radiation which is reflected? It is this parameter rather than light velocity which is important. The solution lies in the maximum frequency response of the electron gas, which is the plasmon frequency w p and is calculated in a straightforward way. If light frequency is greater than w p then the electron gas in the metal can no longer respond and the reflectivity tends to zero. The problem you are posing is that if the wave is guided by the metal then this implies that the charge resides on the metal surface. As the wave travels at light velocity, then charge supplied from outside the system would have to travel at light velocity as well, which is clearly impossible. The answer is found by considering the nature of conduction in metals. Here we have a lattice of positively charged atoms surrounded by a sea of free electrons which can move in response to an electric field. This response can be very rapid and results in a polarisation of charge at the surface and through the metal. At frequencies greater than w p the electron gas cannot respond which is the reason for the transparency of metals to ultra-violet radiation. However for frequencies used in communications the electron gas can easily respond to the radiation and reflectivity is unity. If
a poor conductor is used instead of a metal, i.e. there are no freely
conducting electrons, then there is no polarisation, and as you point out
charge cannot enter the system, and there can be no surface field.
Consequently reflection of the radiation will not occur at these low frequencies
and there is no waveguide action. I
hope that these comments provide a satisfactory explanation. Yours sincerely, [signed] M Pepper |
|
August 23, 1993 Dear Raeto West, I write with reference to
your letter of August 19. Your description of the process is correct; as a
TEM wave advances so charge within the conductor is polarised and the disturbance
propagates at right angles to the direction of propagation of the wave ....
.... Yours sincerely, M Pepper |
|
Portrait of a Drivelmaster… A one-electron man. Can’t handle a whole row of them. Throwing
glasses at stone houses Google search for “Pepper FRS”
“The point about the Catt Anomaly has, says Ivor, nothing
to do with his theory. It is an anomaly between rival textbooks and
professors [Pepper and McEwan]. They will answer his polite query
in their condescending authoritative manner until they are told that
their ‘explanation’ is the exact opposite of that taken by other authors and professors . Then
they cannot be induced to communicate with one another to resolve
the problem.” – Editorial, Electronics
World, August 2003, p3. As the wave
travels at light velocity, then charge supplied from
outside the system would have to travel at light velocity as well,
which is clearly impossible.
|