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uk.tech.digitaltv (Digital TV  General) (uk.tech.digitaltv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions. 

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#1




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




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




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




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 (Î¼ (permeability) times Îµ (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




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 electromagnetic 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 electromagnetic 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 busstop conversation between another student who'd been present with my then girlfriend, gave me something of a reputation for the subject. But I wouldn't want to be asked to prove it now! 
#6




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




OT question
replying to Bill Wright, Iggy wrote:
Lies, Liars and Frauds...to put it precisely. Space "science" (laughable nonscience) 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/ukdiy...n1258527.htm 
#8




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




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




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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