Tag Info

New answers tagged

2

So this is a many-part question. If you look at that diagram, in fact, you will see that the pressure peaks and troughs (the circles) do not "stack up": nowhere are they intersecting. So in fact the only effect in this diagram is that the pressure for the circle of radius $r$ is actually decreasing like $1/r$ as the circle gets bigger. The intensity, which ...


0

Where does the energy go when light is redshifted? It doesn't go anywhere. Let's say we're motionless with respect to some source which is emitting a stream of photons. We agree that the photons have some energy E=hf. Now let's say I push you such that you're moving away from the source. You now claim that the photons are redshifted, but those photons ...


1

Nobody ever said that different observers have to agree on the energy of a photon (or anything else). The invariant quantity is energy minus momentum (i.e. rest mass), which is equal to zero whether the photon is red or green. (Edited to add: I see now that userLTK already said as much in a comment.)


0

A simpler answer. Things which move towards you sound higher pitched (higher frequency), things moviing away sound lower pitched (lower frequency). If something moves at the speed of sound or faster, you won't hear it until it gets to you. (Sonic Boom) With light, it's something like the same principle. Something moving towards you has a blue shift ...


0

2nd ATTEMPT (after taking advice from Sofia's answer) Let us consider the experiment in the inertial rest frame of the pulses as they move along the $x$-axis in the $x+$ direction. In this frame the source is moving along the $x$-axis in the $x-$ direction at constant velocity $-s$. At all times $t_*$ the receiver is accelerating towards $x-$ with ...


7

Yes, the sound can be reversed. Thanks to JiK, we have this animation (Python source code) of a supersonic jet moving forwards that can illuminate what is going on: The red circle represents the first sound produced by the object, the blue circle the second sound produced by the object and the remaining (black) circles representing the sounds produced ...


1

As you stated, the observer would not hear anything as the plane approached him. If fact, he still would not hear anything until the plane had past by since it takes some time for the sound to travel from the plane to the observer. In answer to your question; no, you would not hear the sound backwards since you still hear the sound in the same sequence as it ...


2

Light has a frequency of approx. 1e15Hz. Can light be transmitted in a hollow copper tube? Yes. No need to go relativistic. Can objects move at near the speed of light in a coax cable with inner conductor? No. They can't move in there, at all, not even at walking speed. Does any of this has anything to do with photons? No. Your experiment does have a ...



Top 50 recent answers are included