Ghanem9 Posted November 30, 2007 Report Share Posted November 30, 2007 is it just me or are other ibers facing trouble with the waves topic!!!!!!!!!!!! there are some parts i get and some i dnt... it prolly the teacher he's in such a hurry these days we're even taking physics instead of english B (since we're done with teh material) if anyone can help explain and answer this question for me it would be of great help! i'll try to ask the teacher (if he's got time...he's part-time) here's the Q: (a) (i) State the principle of superposition. ................................................................................ .......................................... ................................................................................ .......................................... Two loudspeakers S1 and S2 are connected to the same output of a frequency generator and are placed in a large room. Sound waves of wavelength 40 cm and amplitude A are emitted by both loudspeakers. M is a point distance 550 cm from both S1 and S2. Point P is a distance 560 cm from S1 and 580 cm from S2. (there's a picture... bt i dnt know how to add it me not so gr8 with forum....) (ii) State and explain what happens to the loudness of the sound detected by a microphone when the microphone is moved from point M to point P. ................................................................................ .......................................... ................................................................................ .......................................... ................................................................................ .......................................... ................................................................................ .......................................... ................................................................................ .......................................... (iii) Referring to the diagram above, the amplitude of the wave emitted by S1 is now increased to 2A. The wave emitted by S2 is unchanged. Deduce what change, if any, occurs in the loudness of the sound at point M and at point P when this change in amplitude is made. at point M: ................................................................................ ..................... ................................................................................ ..................... at point P: ................................................................................ ..................... ................................................................................ ..................... (iv) The loudspeakers are now replaced with two monochromatic light sources. State the reason why bright and dark fringes are not observed along the line PM. ................................................................................ .......................................... Waves of frequency f and speed c are emitted by a stationary source of sound. An observer moves along a straight line towards the source at a constant speed v. (d) State, in terms of f, c and v, an expression for (i) the wavelength of the sound detected by the observer. ................................................................................ .......................................... (ii) the apparent speed of the wave as measured by the observer. ................................................................................ .......................................... The observer carries a second source of sound, producing waves of the same actual frequency and speed as the stationary source. Whilst moving, the observer detects a beat frequency of 6.0 Hz for sound waves emitted by the sources of frequency 500 Hz and speed 340 ms–1. (e) (i) Describe what is meant by beats. ................................................................................ .......................................... ................................................................................ .......................................... ................................................................................ .......................................... (ii) Calculate the speed v of the observer. ................................................................................ .......................................... ................................................................................ .......................................... ................................................................................ .......................................... ................................................................................ .......................................... Reply Link to post Share on other sites More sharing options...
Forester Posted December 29, 2007 Report Share Posted December 29, 2007 it would be great if u add the marks allocated to each question, this way we know if a short or long answer is required.ii) for this question, please disregard what I said about the doppler effect earlier. this is just simple superposition. The loudness would go up then down (zero) then up again.iii) the loudness would not be zero at some parts, it will fluctuate between 1A and 3A. (forgive me, I am not using the correct terminology, it's the holidays haven't revised for a long time)From what I can see, these questions are the basics. If you are having trouble with these, then I advise you to seek a professional tutor. Reply Link to post Share on other sites More sharing options...
ezex Posted December 30, 2007 Report Share Posted December 30, 2007 (edited) it would be great if u add the marks allocated to each question, this way we know if a short or long answer is required.ii) for this question, please disregard what I said about the doppler effect earlier. this is just simple superposition. The loudness would go up then down (zero) then up again. iii) the loudness would not be zero at some parts, it will fluctuate between 1A and 3A. (forgive me, I am not using the correct terminology, it's the holidays haven't revised for a long time) From what I can see, these questions are the basics. If you are having trouble with these, then I advise you to seek a professional tutor. Well let me try to correct some things. I wouldn't exactly put the answer you put for ii), simply because you don't know if it's superposition, destructive, or neither. This seems to be kind of like the Double-Slit Young experiment, though it's not. What you have to consider, is that for there to be a superposition, d1 plus d2 (distances from the two points) has to equal *wavelenght, n being any order, 1st, 2nd, 3rd, etc...In this equation you have everything except for n. If n comes out to be a whole number, then you have superposition. If it's a fraction with .5 in it, then it's destructive, and if its netiher, then it's just non of the above Let me keep reading the question...i lost track of it Allright, I cheked and you get that n = 28.5 so it's destructive and you don't hear anything for the question asking about if the amplitude increases to 2A...well I could give you a general answer, but this is one of the things I don't get. We were doing waves last week so i have most of the material fresh. Eh...I can't exactly answer this one yet without saying things that might be wrong so I'll skip it for now (my best guess is that amplitude has no effect on the experiment, but I don't have evidence to back it up). Question iv) Ok, now we know that for a clear pattern to show, the 2 sources have to have the same pure frequency, or else the pattern will be unrecognizable. Since this is monochromatic light, there is no clear pattern, and dark and bright fringes are not visible. Question d) This is the doppler effect Some background: frequency1 = frequency0*(velocity of wave +/- velocity of observer)/(velocity of wave -/+ velocity of source), in this case velocity of source is 0, frequency is f, velocity of the wave is c and the velocity of the obvserver is v. i) frequency = f[(c+v)/c)], it's plus because the obsverver is moving towards the source (if the source moves towards the obvserver its minus, simply because what you are doing is thinking about the situation: if the objects are closing in then you obviously want to hear more frequency so the top has to be plus and botom minus, if you want to hear less, signs are opposite) now we know that speed of the wave = frequency * wavelenght, therefore, wavelenght = c/(f[(c+v)/c)]) All right I'm going to go check on some other things in my book to try to answer the other parts of the question, and feel free to post back if you don't understand a part, it takes a while to understand. Edited December 30, 2007 by ezex Reply Link to post Share on other sites More sharing options...
Forester Posted December 30, 2007 Report Share Posted December 30, 2007 I did this last term, so sorry for the mistakes...I'm not particularly good with physics anyways, one of my weaker subjects. Reply Link to post Share on other sites More sharing options...
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