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Thread ID: 55026	2005-03-01 00:36:00	How fast is the speed of light... in GB/s?	hamstar (4)	PC World Chat

Post ID	Timestamp	Content	User
329202	2005-03-02 02:48:00	My light travels 300 km each second. Strangely enough, a standard measure in radar work is 1ms = 150 km. That is the time for an electromagnetic pulse to go and return , a total travel distance of 300 km. Because visible light and radar are simply photons travelling at different wavelengths. X rays, gamma rays, sound waves are all photons but at different energy levels.	Winston001 (3612)
329203	2005-03-02 03:03:00	That's a lawyer's view, so not related to the physics or the real world. :p Photons don't have wavelengths. They have energy levels. Visible light, invisible light, television transmissions, radar, are all electromagnetic waves in a continuous spectrum. And they travel at the speed of light in whatever medium they are in. Sound waves are not photons, nor related to EM phenomena in any way. They are mechanical vibrations. It is possible to have sound waves at "radio" frequencies. ("ultrasonics") They are mechanical vibrations at the high frequency, and they propagate at the speed of sound in the medium.	Graham L (2)
329204	2005-03-02 07:35:00	Ok guys - who added sound waves to my post? Come on - own up . Sheesh Oh well . . . . . . . . . . I abase myself Graham . I am not worthy . :blush: Oh, by the way, could you give us a quick exposition on the wave/particle duality please . Frankly I get a headache every time I try to read about it .	Winston001 (3612)
329205	2005-03-02 07:44:00	Ok, very quickly then, the photo electric effect as shown by Einstein demonstrates the particle or photon nature of light. Shine the same light through a narrow slit and observe diffraction patterns explained by the wave nature of light. Did you want the maths winston?	Terry Porritt (14)
329206	2005-03-02 07:46:00	Ok guys - who added sound waves to my post? Come on - own up . Sheesh Oh well . . . . . . . . . . I abase myself Graham . I am not worthy . :blush: Oh, by the way, could you give us a quick exposition on the wave/particle duality please . Frankly I get a headache every time I try to read about it . This is known as the deBroglie wavelength = h/p Since in the macroscopic world momentum, p, tends to be large ( even when particles have the smallest of velocities) deBroglie wavelengths of large objects are minute and impossible to measure, but for atomic particles or smaller a noticable property can be calculated,anyway I wont go on,to the unlearned ear it can get tedious and headach inducing . ;)	Cicero (40)
329207	2005-03-02 08:25:00	Visible light, invisible light, television transmissions, radar, are all electromagnetic waves in a continuous spectrum. And they travel at the speed of light in whatever medium they are in. A quick look at a basic book on light physics says that the speed of light is inversely proportional to the refractive index of the medium. The speed of light is constant in any given medium, but not constant between mediums.	user (1404)
329208	2005-03-02 08:35:00	George, you must have some very slow "fast" transistors . Are they made out of wood or lead instead of silicon or germanium? Old technology TTL normally switched in about 5-6 nanoseconds . Some of the new technology transistors can switch in picoseconds . String would switch faster than 300 microseconds . Your light seems to be running a bit slow too . My light travels 300 km each second . Strangely enough, a standard measure in radar work is 1ms = 150 km . That is the time for an electromagnetic pulse to go and return , a total travel distance of 300 km . The difference between air and vacuum is small enough to be neglected (usually) . I suspect you are having trouble with powers of ten, often called "orders of magnitude" . They do make a difference . ;) I knew that was coming . I wasn't thinking too much when I wrote this . I do actually know about powers of ten etc . Of course . And I just got that off the first datasheet that said "ultra high speed" . . . :o	george12 (7)
329209	2005-03-02 08:52:00	Did you want the maths winston? I got 64% in School Certificate maths and I'm convinced they must have marked someone elses paper for that good a result. Thankyou, but no thankyou Terry. Actually I have been expecting your learned wisdom on this topic. Cheers Winston	Winston001 (3612)
329210	2005-03-02 08:54:00	This is known as the deBroglie wavelength = h/p Since in the macroscopic world momentum, p, tends to be large ( even when particles have the smallest of velocities) deBroglie wavelengths of large objects are minute and impossible to measure, but for atomic particles or smaller a noticable property can be calculated,anyway I wont go on,to the unlearned ear it can get tedious and headach inducing. ;) Tom - you never cease to amaze me. But I'm sorry I asked - migraine coming on. It's the deBroglie effect no doubt. :badpc:	Winston001 (3612)
329211	2005-03-02 09:24:00	A quick look at a basic book on light physics says that the speed of light is inversely proportional to the refractive index of the medium. The speed of light is constant in any given medium, but not constant between mediums. Correct, though we have to distinguish between group and wave velocity :) Just to add in some relativistic considerations, years ago it was thought possible to measure the velocity of light, and indeed from Roemer's astronomical determination onwards, with increasing sophistication the velocity of light was measured by various optical/mechanical/electrical means. In those days, length was defined by a physical length standard like the yard or metre, and time by the mean sideral second. Thus it was possible to measure velocity of light using those standards. However as physical standards became more sophisticated and less dependent on artifacts, any attempt to measure the speed of light is now really a measurement of distance. Once a quantity is defined as a standard, eg ascribe a fixed value to the speed of light, it ceases to be measurable by definition, and since time measurement is traceable to atomic standards, then distance=velocity of light c x time. At one time it was postulated that an all pervading 'ether' existed, and that it should be possible to measure the speed of light in two directions at right angles so as to determine the relative speed of the earth through the ether. Attempts to do this by Michelson and Morley showed no difference, and this spelt the death knell of the ether theory :)	Terry Porritt (14)
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