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DK2ZA > INFO 15.08.02 23:13l 98 Lines 3207 Bytes #999 (30) @ WW
BID : F8CDB0MRW02N
Read: DB0FHN GUEST
Subj: re: speed of light (OZ1DWF)
Path: DB0FHN<DB0ZWI<DB0HDF<DB0ERF<DB0SON<DB0MRW
Sent: 020815/2351z @:DB0MRW.#BAY.DEU.EU [Wunsiedel, JO60AB] Bcm1.46 LT:030
From: DK2ZA @ DB0MRW.#BAY.DEU.EU (Helmut)
To: INFO @ WW
X-Info: Sent with login password
Leif, OZ1DWF, asked the following question:
> OZ1DWF > SIENCE 15.08.02 16:20l 69 Lines 2690 Bytes #30 (0) @ WW
> BID : 7841_OZ1DWF
> Read: DK2ZA
> Subj: ??!!?? Speed of light thru one meter ??!!??
> Path: DB0MRW<DB0ERF<DB0ROF<DB0AIS<DB0ZDF<DB0LJ<LX0HST<HA3PG<JE7YGF<JM1YSB<
> 7M3TJZ<OZ2DIZ<OZ2BOO
> Sent: 020815/1407Z @:OZ2BOO.FRH.JYN.DNK.EU #:41495 [Frederikshavn] FBB7.00e
> From: OZ1DWF@OZ2BOO.FRH.JYN.DNK.EU
> To : SIENCE@WW
> # System : Amateur Radio Packet
> # Sub system : TCP/IP personal e-mail <=> packet.
> # Sysop : OZ1DWF Leif Aaen
> # Packet mail : OZ1DWF@OZ2BOO.FRH.JYN.DNK.EU
> # E-mail : oz1dwf@qsl.net
> # MSN : oz1dwf@hotmail.com
> # ICQ : 160384299
> # Homepage1 : http://www.qsl.net/oz1dwf/
> # Homepage2 : http://www.Geocities.com/oz1dwf/
> # HAM IP : 44.145.0.41
> # On : 15-08-02 16:05:42
> # UTC: 15-08-02 14:05:42
> Greetings out there.
> --------------------
> I was working with some studies, were the length of one meter came into
> question. Defination of one meter then given as:
> 1 Meter = Speed of light in 1/229,792,458 sec. in vacum.
> Well. Infrared is slower than Ultra, so did someone forget to annonce the
> correct frequency of the light ?
> -Since light travels with different speed, this messurement may result in
> some inaccuracy.
> The question is perhaps notthing at all, because we're talking a wide
> spectra of light, or reference for a specific source, like a
> He-Li-lasergun.
> Well. I don't have such a precise timer, nor finger to trick a manuel
> stopwatch. My contacts in my electric installation is too slow too, but
> when such a detailed messurement in split-second is mentioned, I wonder why
> the specification of witch kind of light to be used, is hitten as a major
> secret, hi.
> -Just thinking, teaching material not allways gives answars, but raise
> questions too :-)
> Vy 73 de OZ1DWF, Leif
The answer is:
The speed of light in a vacuum is NOT dependent on its wavelength
(or frequency or color). In fact, the speed of all kinds of
electromagnetic radiation from the longest radiowaves up to the
shortest gamma ray bursts from space is exactly the same in a
vacuum.
It is c = 299 792 458 m/s
This value is exact, i.e. it contains no measurement error, because
it is a DEFINITION.
But can we define the speed of light?
======
Sure! If we adjust the legth of 1 meter so that light in a vacuum
travels exactly 299 792 458 meters in one second. This has been done
and agreed upon internationally.
So today 1m is no longer 1/40 000 000 the length of the equator as it
was 200 years ago, but it is the distance in a vacuum covered by light
(any wavelength!) in 1/299 792 458 of a second.
I should add that in a medium (glass, water, air ...) the speed of light
is always slower than in a vacuum and that it depends on the wavelength.
This effect is called dispersion and is very important for fiber optics.
The dispersion of electromagnetic waves in a vacuum however is zero!
vy 73 de Helmut, DK2ZA
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