what does in phase and out of phase waves mean and what effect does it have with interference?

Question

what does in-phase sound waves meaning?
and what does it have to do/ what happens when in phase waves meet?
could you also tell me what out of phase waves are?

Answer 1

Waves with the same frequency can be out of phase in a given point when their maxima (or minima) are not coincident.

This may happen because they traveled different distances to reach the point when they superimpose. When they are inphase the resultant amplitude is the sum of the amplitudes. When they are completely out of phase it's the difference of amplitudes but you can have all the intermediate possibilities, that is, waves that are partially out of phase

Answer 2

Not a very nice question. I don't like the the answer D very much as 'nature' isn't a very precise term. I agree that C being 'wrong' is interesting. After all for two waves to interfere they are going to be travelling in the same medium and hence will have the same speed. I'll ignore light as light always gets very awkward but how about sound waves? Interference means that the pressure waves are co-located and hence must be in the same medium. Does that make it a necessary condition for interference? I suspect not though I can't give an example. Maybe something involving a sudden change in density which would result in a transient condition where the two pressure waves can briefly have different speeds? A and B are obviously wrong, D the correct answer is just too vague and wooly. I wish I could site a decent example for C where speeds are not the same.

Answer 3

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Interesting question. First, remember interference is just the superposition of waves. If there are two continuous waves of equal amplitude and different (and unrelated) frequencies, at any given moment there will be points where the amplitudes are equal-opposite producing destructive interference, and equal-same producing constructive interference. (In ref. 1, these are the zero crossings and peaks of the resultant in the lower-left window.) In ref. 2 are two examples of interference that are useful to this concept. In "Two sine waves travelling in the same direction: Constructive and Destructive Interference" you see that two waves of magnitude A traveling at different speeds in the same direction combine such that at any given point the amplitude varies from 0 to ±2A. In "Two sine waves with different frequencies: Beats" you see the same result (but on a different time scale). Some authorities don't like to consider differing frequencies as interfering but that's what they do. What you don't get with different frequencies interfering are nice clear lines of nodes and antinodes. Every node and antinode is in continual motion, since the relative phase of the waves at any given point is changing. The reason you don't have any effects from adjacent channels is (1) the receiver can tune out the unwanted signal and (2) even if there were interference the frequency of the resultant would be beyond the range passed by the rest of the receiver (the IF and audio/video portions). You can get interference from signals that are within the channel even if not exactly the same frequency; that's why the FCC allocates channels such that nearby stations don't share the same channel. EDIT: An interesting answer from frothuk. I take "same nature" to mean both are sound or light or whatever and both are either transverse or longitudinal (sound can be either). But is indeed woolly. About different speeds, consider water waves, which can interfere. This makes C definitely false.

Answer 4

sound waves are alternate compressions and rarefactions of the air (or other medium)



In phase means the compression parts of waves of the same wavelength from two sources arrive at the point of interest at the same time, and thereby reinforce each other (add together)



Out of phase means that the compression from one wave and the rarefaction from the other wave arrive at the point of interest at the same time, and tend to subtract from each other.