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Hi Bruce & All, Sept 23, 2012
Thanks for the enlightenment.
=20
But, when light is involved, there are bound to be dark corners.=20
I stumbled across one curious way to measure the speed of light, =
when trying to guestimate the relative magnitude of charge on a coaxial =
cable. This method involves a parallel plate condenser and, although it =
would be very inconvenient to do so, the measurements could be made =
while the apparatus was in complete darkness.
Without going into detail, with charge Qm & Qs and voltage Vm & Vs =
known either by calculation or measurment, where lowcase m & s signify =
electromagnetic units (E.M.U.) and electrostatic units (E.S.U.) =
respectively, one can then calculate capicitance (C) in the two systems =
of units, Cm & Cs.
Cm/Cs equals the speed of light, expressed as cm/sec, squared; i.e. =
Cm/Cs=3D c^2 =20
and c =3D sqrt(Cm/Cs).
Perhaps someone can explain what is behind this (to me) entirely =
unexpected relationship. I can send a scan of the relevant pages if =
applicable.
Yt, Dave Webster, Kentville
----- Original Message -----=20
From: Bruce Stevens=20
To: naturens@chebucto.ns.ca=20
Sent: Friday, September 21, 2012 10:40 PM
Subject: Re: [NatureNS] Velocity of light
Dave,
Nothing you have said is incorrect. A vector is convenient to =
represent a quantity that has both a magnitude and direction. Speed is =
simply the magnitude (scalar portion) of a velocity vector. If we call =
the light vector C, The speed of light (3x10^8 m/s), denoted by c, is =
the magnitude of the light vector, or mathematically, ||C||. It is only =
necessary to treat light propagation as a vector if the math requires =
it. In many situations the speed suffices.=20
Hope this illuminates the situation.
Bruce
On Fri, Sep 21, 2012 at 7:44 PM, David & Alison Webster =
<dwebster@glinx.com> wrote:
Dear All, Sept 21, 2012
The recent discussion about transmission of electricity, reading =
of HEAT and reading some of Energy... brings to the forefront a question =
that has nagged me for decades. Perhaps someone can clarify.
In the typical elementary physics text we are told that velocity =
is a vector quantity, and to quote one text "velocity... may be defined =
as the rate of change of position in a given direction". But "In cases =
where the direction of motion does not require to be considered , the =
term speed is employed to express the rate of travelling."
Based on the above I would think that the rate of movement of =
light should be called speed, i.e. speed of light but I think it is =
always called velocity.
For example, if light from the sun is reflected from two 45o mirrors =
then a beam of light could be directed from the earth back to the sun =
and, the velocity would then be minus 3 x 10^10 cm/sec. Or if variously =
scattered or reflected then the velocity, relative to the initial sun to =
earth direction, would always be less than 3 X 10^10 and after several =
reflections might be zero.
Is there some good reason why the speed of light is termed =
velocity of light ? Or is it called velocity because the textbook =
authors forget what they said in chapter one by the time they write =
chaper eleven ? (And they all copy from each other)
Yt, Dave Webster, Kentville=20
--=20
Bruce Stevens
Maryvale, NS
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2221 / Virus Database: 2441/5278 - Release Date: =
09/19/12
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content=3D"text/html; charset=3Diso-8859-1" =
http-equiv=3DContent-Type>
<META name=3DGENERATOR content=3D"MSHTML 8.00.6001.19298">
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT size=3D2>Hi Bruce & All, =
=20
=
=20
Sept 23, 2012</FONT></DIV>
<DIV><FONT size=3D2> Thanks for the =
enlightenment.</FONT></DIV>
<DIV><FONT size=3D2> </FONT></DIV>
<DIV><FONT size=3D2> But, when light is involved, =
there are=20
bound to be dark corners. </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> I stumbled across one curious way =
to=20
measure the speed of light, when trying to guestimate the relative =
magnitude of=20
charge on a coaxial cable. This method involves a parallel plate =
condenser=20
and, although it would be very inconvenient to do so, the measurements =
could be=20
made while the apparatus was in complete darkness.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2> Without going into detail, =
with charge=20
Qm & Qs and voltage Vm</FONT> <FONT size=3D2>& Vs =
known=20
either by calculation or measurment, where lowcase m & s signify=20
electromagnetic units (E.M.U.) and electrostatic =
units (E.S.U.)=20
respectively, one can then calculate capicitance (C) in the two =
systems of=20
units, Cm & Cs.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> Cm/Cs equals the speed of light, =
expressed=20
as cm/sec, squared; i.e. Cm/Cs=3D c^2 </FONT></DIV>
<DIV><FONT size=3D2> and c=20
=3D sqrt(Cm/Cs).</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> Perhaps someone can explain what =
is behind=20
this (to me) entirely unexpected relationship. I can send a scan of the =
relevant=20
pages if applicable.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Yt, Dave Webster, Kentville</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; =
PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"=20
dir=3Dltr>
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: =
black"><B>From:</B>=20
<A title=3Dm.bruce.stevens@gmail.com=20
href=3D"mailto:m.bruce.stevens@gmail.com">Bruce Stevens</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Dnaturens@chebucto.ns.ca=20
href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</A> =
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Friday, September 21, =
2012 10:40=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [NatureNS] =
Velocity of=20
light</DIV>
<DIV><BR></DIV>Dave,
<DIV><BR></DIV>
<DIV>Nothing you have said is incorrect. A vector is convenient to =
represent a=20
quantity that has both a magnitude and direction. Speed is simply the=20
magnitude (scalar portion) of a velocity vector. If we call the light =
vector=20
C, The speed of light (3x10^8 m/s), denoted by c, is the magnitude of =
the=20
light vector, or mathematically, ||C||. It is only necessary to treat =
light=20
propagation as a vector if the math requires it. In many situations =
the speed=20
suffices. </DIV>
<DIV><BR></DIV>
<DIV>Hope this illuminates the situation.
<DIV><BR></DIV>
<DIV>Bruce<BR><BR>
<DIV class=3Dgmail_quote>On Fri, Sep 21, 2012 at 7:44 PM, David & =
Alison=20
Webster <SPAN dir=3Dltr><<A href=3D"mailto:dwebster@glinx.com"=20
target=3D_blank>dwebster@glinx.com</A>></SPAN> wrote:<BR>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; =
PADDING-LEFT: 1ex"=20
class=3Dgmail_quote>Dear All, =
=20
Sept 21, 2012<BR> The =
recent=20
discussion about transmission of electricity, reading of HEAT and =
reading=20
some of Energy... brings to the forefront a question that has nagged =
me for=20
decades. Perhaps someone can clarify.<BR><BR> In the =
typical=20
elementary physics text we are told that velocity is a vector =
quantity, and=20
to quote one text "velocity... may be defined as the rate of change =
of=20
position in a given direction". But "In cases where the direction of =
motion=20
does not require to be considered , the term speed is employed to =
express=20
the rate of travelling."<BR><BR> Based on the above I =
would=20
think that the rate of movement of light should be called speed, =
i.e. speed=20
of light but I think it is always called velocity.<BR>For example, =
if light=20
from the sun is reflected from two 45o mirrors then a beam of light =
could be=20
directed from the earth back to the sun and, the velocity would then =
be=20
minus 3 x 10^10 cm/sec. Or if variously scattered or reflected then =
the=20
velocity, relative to the initial sun to earth direction, would =
always be=20
less than 3 X 10^10 and after several reflections might be=20
zero.<BR><BR> Is there some good reason why the speed of =
light=20
is termed velocity of light ? Or is it called velocity because the =
textbook=20
authors forget what they said in chapter one by the time they write =
chaper=20
eleven ? (And they all copy from each other)<BR>Yt, Dave Webster, =
Kentville=20
<BR></BLOCKQUOTE></DIV><BR><BR clear=3Dall>
<DIV><BR></DIV>-- <BR>Bruce Stevens<BR>Maryvale, =
NS<BR></DIV></DIV><A></A>
<P align=3Dleft color=3D"#000000" avgcert??>No virus found in this=20
message.<BR>Checked by AVG - <A=20
href=3D"http://www.avg.com">www.avg.com</A><BR>Version: 2012.0.2221 / =
Virus=20
Database: 2441/5278 - Release Date: =
09/19/12</P></BLOCKQUOTE></BODY></HTML>
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