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  #1  
Old December 24th 17, 08:43 PM posted to uk.tech.digital-tv,uk.d-i-y
Bill Wright[_3_]
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Default OT question

What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?

Bill
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  #2  
Old December 24th 17, 08:59 PM posted to uk.tech.digital-tv,uk.d-i-y
newshound[_3_]
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Posts: 24
Default OT question

On 24/12/2017 20:43, Bill Wright wrote:
What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?

Bill


Start here

https://en.wikipedia.org/wiki/Electr..._wave_equation

then look up permittivity and permeability of free space
  #3  
Old December 24th 17, 10:01 PM posted to uk.tech.digital-tv,uk.d-i-y
Indy Jess John
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Posts: 1,307
Default OT question

On 24/12/2017 20:43, Bill Wright wrote:
What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?

Bill


You have to bear in mind that the metre is an arbitrary distance based
on the circumference of the Earth, and a second was a fraction of the
duration of the Earth's orbit, finally fixed as a number that is
9,192,631,770 cycles of the radiation produced by the transition between
two levels of the caesium 133 atom.

Admittedly we have got nothing better to describe the speed of light,
but it does explain why that speed when calculated isn't a conveniently
memorable number.

Jim

  #4  
Old December 24th 17, 10:28 PM posted to uk.tech.digital-tv,uk.d-i-y
Graham Nye
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Posts: 7
Default OT question

On 24/12/2017 20:43, Bill Wright wrote:
What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?


To save you wading through a load of vector partial differential
equations have a look at the equation under the text "which identify"
in the section:
https://en.wikipedia.org/wiki/Maxwell's_equations#Vacuum_equations,_electromagne tic_waves_and_speed_of_light

The summary is:
Speed of light (or other EM radiation) is one over the square root
of (μ (permeability) times ε (permittivity)).

Permeability and permittivity are measures of the magnetic and
electric properties (respectively) of a material.

A common practice is to take the permeability and permittivity of a
material and divide them by the permeability and permittivity of a
vacuum. The resulting ratios are known as the relative permeability
and relative permittivity respectively.

For people familiar with electronic components relative permittivity
is also known as dielectric constant in capacitors. It's the factor
by which the capacitance is multiplied due to using a given dielectric
material as an insulator rather than vacuum (or, more practically, air).

Some more reading:
https://en.wikipedia.org/wiki/Permeability
https://en.wikipedia.org/wiki/Permittivity

The number you get will depend on the units you use. If you use something
other than SI units (metres, kilograms, seconds, etc) you'll get a
different number, e.g. 186,282 miles per second. (But it should be the
same speed, just expressed in different units.)


--
Graham Nye
news(a)thenyes.org.uk
  #5  
Old December 24th 17, 10:36 PM posted to uk.tech.digital-tv,uk.d-i-y
Java Jive[_2_]
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Posts: 1,774
Default OT question

On 24/12/2017 20:43, Bill Wright wrote:

What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?


The electro-magnetic behaviour of space is described by Maxwell's
Equations. As newshound has suggested, it is possible to show* that a
wave equation is a possible solution of Maxwell's Equations, and that
the speed of the resulting wave would be equal to ...
1 / sqroot( permittivity of space * permeability of space)
.... and that this value is exactly equal to the measured speed of light
in space. This is how we know that light is an electro-magnetic wave.

* This is science speak:

It is trivial to show that = an undergrad can prove it
It is easy to show that = a postgrad can prove it
It may be proved that = The prof can prove it

In this particular case, I was able to prove it at uni, and did so
during a physics tutorial, which, I discovered much later from a
bus-stop conversation between another student who'd been present with my
then girl-friend, gave me something of a reputation for the subject.
But I wouldn't want to be asked to prove it now!
  #6  
Old December 24th 17, 10:53 PM posted to uk.tech.digital-tv,uk.d-i-y
Norman Wells[_6_]
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Posts: 984
Default OT question

On 24/12/2017 22:01, Indy Jess John wrote:
On 24/12/2017 20:43, Bill Wright wrote:
What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?

Bill


You have to bear in mind that the metre is an arbitrary distance based
on the circumference of the Earth, and a second was a fraction of the
duration of the Earth's orbit, finally fixed as a number that is
9,192,631,770 cycles of the radiation produced by the transition between
two levels of the caesium 133 atom.

Admittedly we have got nothing better to describe the speed of light,
but it does explain why that speed when calculated isn't a conveniently
memorable number.


I think what he's asking is why it's a constant, ie what makes it so,
and why it is what it is rather than something else?

Got any answer?
  #7  
Old December 25th 17, 05:14 AM posted to uk.tech.digital-tv,uk.d-i-y
Iggy[_2_]
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Posts: 1
Default OT question

replying to Bill Wright, Iggy wrote:
Lies, Liars and Frauds...to put it precisely. Space "science" (laughable
non-science) is the biggest bunch of contradictions ever. They claim
authority, simply make an outlandish statement, never provide any proof nor
duplication and the droolers obey. They tell us only what Real Science has
duplicated and measured, though their patently ridiculous Big Bang crushed it
all. Therefore, your speeds can't exist...according to them. However, your
speeds must and do exist...according to them.

--
for full context, visit https://www.homeownershub.com/uk-diy...n-1258527-.htm


  #8  
Old December 25th 17, 08:18 AM posted to uk.tech.digital-tv,uk.d-i-y
The Natural Philosopher[_2_]
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Posts: 639
Default OT question

On 24/12/17 20:43, Bill Wright wrote:
What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?

Bill


Not everything has a cause. Some things Just Are.

God was the traditional explanation of course.


--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx

  #9  
Old December 25th 17, 08:19 AM posted to uk.tech.digital-tv,uk.d-i-y
The Natural Philosopher[_2_]
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Posts: 639
Default OT question

On 24/12/17 20:59, newshound wrote:
On 24/12/2017 20:43, Bill Wright wrote:
What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?

Bill


Start here

https://en.wikipedia.org/wiki/Electr..._wave_equation

then look up permittivity and permeability of free space


But that doesnt do more than transform the question into 'why is that
the value of the permittivity and permeability of free space'?



--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx

  #10  
Old December 25th 17, 08:21 AM posted to uk.tech.digital-tv,uk.d-i-y
The Natural Philosopher[_2_]
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Posts: 639
Default OT question

On 24/12/17 22:53, Norman Wells wrote:
On 24/12/2017 22:01, Indy Jess John wrote:
On 24/12/2017 20:43, Bill Wright wrote:
What are the parameters that set the speed of electromagnetic
transmission in a vacuum? I've googled everywhere but I can't find the
answer. It's easy enough to find the figure but WHY? Why not
29,979,245.8 metres per second or 2,997,924,580 metres per second?

Bill


You have to bear in mind that the metre is an arbitrary distance based
on the circumference of the Earth, and a second was a fraction of the
duration of the Earth's orbit, finally fixed as a number that is
9,192,631,770 cycles of the radiation produced by the transition
between two levels of the caesium 133 atom.

Admittedly we have got nothing better to describe the speed of light,
but it does explain why that speed when calculated isn't a
conveniently memorable number.


I think what he's asking is why it's a constant, ie what makes it so,
and why it is what it is rather than something else?

Got any answer?


Because if it wasnt what it is, the world wouldn't be what it is, and in
all likelihood he wouldn't be wherever here is to ask such damn fool
questions.


--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.

 




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