Yes, vry mch. I used d word signal as i was referring to communication, nothing else.

Statistics: Posted by Swathi — Fri Oct 21, 2011 2:37 pm

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here signal means wave packet right ? something else ?

Statistics: Posted by sandeep — Tue Oct 18, 2011 1:32 pm

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The equation is absolutely correct. Group velocity does exceed the speed of light in such cases and numerous experiments have verified it. You are probably under the assumption that it is not possible for the group velocity to exceed the speed of light because of the upper limit given by Einstein's theory of relativity according to which nothing can travel faster than the speed of light. Even in our case the theory is bound to hold good and it does hold good. This is because even though the group velocity of a wave exceeds the value of 'c' , the velocity of the signal as a whole will never exceed the speed of light and thereby, in no way contradicts Einstein's theory. Signal velocity propogates with a velocity much lesser than the speed of light only. Superluminal communication ( transfer of information through waves travelling faster than the speed of light ) is hence not possible in our case.

Statistics: Posted by Swathi — Sun Oct 16, 2011 7:22 pm

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we know product of phase velocity and group velocity is equal to c^2
but if phase velocity is less than c (speed of light) than group velocity should exceed speed of light. but group velocity can never exceed velocity of light
. is equation is wrong ?

Statistics: Posted by sandeep — Mon Oct 10, 2011 6:04 pm

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