User:LordGorval/my sandbox

This is my very first sandbox ........

Speed of Light and electricity
It seems that the speed of light and the speed of electricity are about the same. Are these two related? --LordGorval (talk) 12:10, 22 April 2009 (UTC)


 * May I point you to the appropriate article: Speed of electricity. The search box is your friend. TheMaster17 (talk) 12:24, 22 April 2009 (UTC)


 * Did you mean Speed of electricity or electromagnetic wave? The latter travels at the speed of light in the vacuum. The former is much slower. Mr.K. (talk) 12:34, 22 April 2009 (UTC)


 * Our article on List of common misconceptions says:


 * "Some textbooks state that electricity within wires flows at nearly (or even exactly) the speed of light, which can give the impression that electrons themselves move almost instantly through a circuit. The electrons in a typical wire actually move at a drift velocity on the order of centimeters per hour (much slower than a snail). The random thermal motions of the electrons are much faster than this, but still much slower than light, and with no tendency to occur in any particular direction. It is the electrical signal that travels almost at the speed of light. The information that a light switch has been turned on propagates to the bulb very quickly, but the charge carriers move slowly."


 * But the article is sorely in need of cites so I don't know if the above is correct. A Quest For Knowledge (talk) 13:07, 22 April 2009 (UTC)


 * Wow, misconceptions are everywhere, including the Speed of electricity article and most of the things on the web that discuss this. When somebody asks for the "speed of electricity", what they usually mean is something like "If I switch on a light, how quickly does the signal travel from switch to light", or "if I send a signal along a wire, how quickly does it reach the receiver".  To answer these questions requires cable theory.  The answer you get depends greatly on the conductivity, boundary impedance, and capacitance of the wire, but it is always far slower than the speed of light.  This article, for example, calculates the speed of signal transmission for a telegraph cable across the Atlantic -- a very fast carrier -- and gets a result of about 2x106 m/sec, or about 1/10000 of the speed of light.  In other words, very fast in human terms (two seconds to cross the Atlantic), but very slow compared to light.  The wires in your home are typically hundreds or thousands of times slower.  For computer equipment, conduction speeds along wires are often an important design factor. Looie496 (talk) 18:21, 22 April 2009 (UTC)


 * The calculation for transatlantic cables may have been accurate in the days of the telegraph, but is not even close when most telephone cables are considered. Up until the mid-70s, transatlantic telephony used either satellite or copper cable.  Satellite experienced noticeable delay, and cable did not.  We can therefore estimate that the round-trip time was less than 100ms.  Therefore for the signal to cross the atlantic, we can estimate a time of 50ms maximum, which is a speed of about 1x108 m/s, or about 1/3 the speed of light.  --Phil Holmes (talk) 09:12, 23 April 2009 (UTC)


 * In a physics lab, we would send pulses down 200' coax cables and measure velocities of 2/3 c. Of course the pulse got smeared some and there are other issues to consider, but Looie's assertion that most wiring would be many orders of magnitude less than c seems unlikely to me too.  Dragons flight (talk) 09:36, 23 April 2009 (UTC)


 * The way to imagine this (crudely) is to imagine an almost frictionless 200' long garden hose and some half-inch ball-bearings. If you stretch out the hose on level ground and roll a ball-bearing down the length of it - it might take 30 seconds to pop out of the other end.  But if you fill the hosepipe full of ball bearings from end to end then if you try to push one ball in at one end - then another one pops out of the other end almost instantaneously.  So even though the individual balls move fairly slowly - the time between stuffing one in one end and a DIFFERENT ball popping out of the other is quite short.   The hose is a wire, the balls are electrons.  The electrons move incredibly slowly - like watching the minute hand move on an analog clock.  But when you push an electron into one end of the wire - a different one pops out the other end with a delay that's about equal to the speed of light.  SteveBaker (talk) 19:06, 22 April 2009 (UTC)


 * Neat! Thanks for answers. The one I understand the best is from SteveBaker. That one I grasp the best and it makes sense on how the "speed of electricity" happens. --LordGorval (talk) 21:15, 22 April 2009 (UTC)