course phy 122 some of the uestions cover things that wwew did not go over in t eh material. {gɥΘ녮assignment #019
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00:08:12 Query introductory set 6, problems 1-10 explain how we know that the velocity of a periodic wave is equal to the product of its wavelength and frequency
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RESPONSE --> velocity can be found by looking at the wavelength (distance from one peak to the next, and multiplying it times the frequency, or number of peaks that pass per second.
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00:08:21 ** we know how many wavelength segments will pass every second, and we know the length of each, so that multiplying the two gives us the velocity with which they must be passing **
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RESPONSE --> hokay
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00:10:01 explain how we can reason out that the period of a periodic wave is equal to its wavelength divided by its velocity
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RESPONSE --> the period is the amount of time that it takes for one wavelength to pass. this can be found by dividing wavelength by the velocity
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00:10:08 ** If we know how far it is between peaks (wavelength) and how fast the wavetrain is passing (velocity) we can divide the distance between peaks by the velocity to see how much time passes between peaks at a given point. That is, period is wavelength / velocity. **
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RESPONSE --> hokay
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00:17:05 explain why the equation of motion at a position x along a sinusoidal wave is A sin( `omega t - x / v) if the equation of motion at the x = 0 position is A sin(`omega t)
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RESPONSE --> this is so because the eqatuion for point x is different only in that it has added the x minus the original and than divided by v.
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00:17:09 ** the key is the time delay. Time for the disturbance to get from x = 0 to position x is x / v. What happens at the new position is delayed by time x/v, so what happens there at clock time t happened at x=0 when clock time was t = x/v. In more detail: If x is the distance down the wave then x / v is the time it takes the wave to travel that distance. What happens at time t at position x is what happened at time t - x/v at position x=0. That expression should be y = sin(`omega * (t - x / v)). } The sine function goes from -1 to 0 to 1 to 0 to -1 to 0 to 1 to 0 ..., one cycle after another. In harmonic waves the motion of a point on the wave (think of the motion of a black mark on a white rope with vertical pulses traveling down the rope) will go thru this sort of motion (down, middle, up, middle, down, etc.) as repeated pulses pass. If I'm creating the pulses at my end, and that black mark is some distance x down in rope, then what you see at the black mark is what I did at time x/v earlier. **
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RESPONSE --> okay
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00:19:25 Query introductory set six, problems 11-14 given the length of a string how do we determine the wavelengths of the first few harmonics?
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RESPONSE --> we use the frequency to figure out how the harmonics are set up. find the frequency to see how long a peak takes to travel the length of the string, and than we can find the wavelengths
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00:22:05 ** As wavelength decreases you can fit more half-waves onto the string. You can fit one half-wave, or 2 half-waves, or 3, etc.. So you get 1 half-wavelength = string length, or wavelength = 2 * string length; using `lambda to stand for wavelength and L for string length this would be 1 * 1/2 `lambda = L so `lambda = 2 L. For 2 wavelengths fit into the string you get 2 * 1/2 `lambda = L so `lambda = L. For 3 wavelengths you get 3 * 1/2 `lambda = L so `lambda = 2/3 L; etc. } Your wavelengths are therefore 2L, L, 2/3 L, 1/2 L, etc.. **
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RESPONSE --> confused, because the math dosen;t quite make as much sense. unless you include lambda, which would make it possible to get theere
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00:22:46 Given the wavelengths of the first few harmonics and the velocity of a wave disturbance in the string, how do we determine the frequencies of the first few harmonics?
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RESPONSE --> I don't know, as it was not covered in the assigned sections
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00:22:57 ** The frequency is the number of crests passing per unit of time. We can imagine a 1-second chunk of the wave divided into segments each equal to the wavelength. The number of peaks is equal to the length of the entire chunk divided by the length of a 1-wavelength segment. This is the number of peaks passing per second. So frequency is equal to the wave velocity divided by the wavelength. **
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RESPONSE --> okay
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00:24:05 Given the tension and mass density of a string how do we determine the velocity of the wave in the string?
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RESPONSE --> use the ension and the mass velocity to determine the amount of force needed to move the sting x smount, then measure how ong it takes the tension to move the string that much
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00:24:19 ** We divide tension by mass per unit length and take the square root: v = sqrt ( tension / (mass/length) ). **
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RESPONSE --> okay,
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00:26:44 gen phy explain in your own words the meaning of the principal of superposition
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RESPONSE --> the principle of superimposition is such that two waves can be together, and if the peaks are at the same time, they combine to form a greater peak, but if they are not, and they are exactally opposite, they cancel out
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00:26:47 ** the principle of superposition tells us that when two different waveforms meet, or are present in a medium, the displacements of the two waveforms are added at each point to create the waveform that will be seen. **
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RESPONSE --> k
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00:26:55 gen phy what does it mean to say that the angle of reflection is equal to the angle of incidence?
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RESPONSE --> pinciples
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00:26:58 ** angle of incidence with a surface is the angle with the perpendicular to that surface; when a ray comes in at a given angle of incidence it reflects at an equal angle on the other side of that perpendicular **
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RESPONSE --> k
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