course PHY 202 x}`¢|͟assignment #020
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22:05:01 **** 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 determine the first few harmonics as follows: 1: 2(L) 2: 2(.5L) 3: 2/3(L)
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22:05:14 ** 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.. FOR A STRING FREE AT ONE END: The wavelengths of the first few harmonics are found by the node - antinode distance between the ends. The first node corresponds to 1/4 wavelength. The second harmonic is from node to antinode to node to antinode, or 4/3. the third and fourth harmonics would therefore be 5/4 and 7/4 respectively. **
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RESPONSE --> pk
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22:07:06 **** 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 --> You determine the frequencies by dividing the velocity by the wavelenghths of the first few harmonics.
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22:07:15 ** 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 --> ok
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22:09:02 **** 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 --> Given the formula: v=sqrt(Ft/m/L) v=velocity Ft=tension of the string m=mass L=length Plug in your knowns and solve for your unknowns.
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22:09:08 ** We divide tension by mass per unit length: v = sqrt ( tension / (mass/length) ). **
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RESPONSE --> ok
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22:10:31 **** gen phy explain in your own words the meaning of the principal of superposition
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RESPONSE --> The principal of superposition desribes what happens when two waves pass the same region at the same time. When determining the sum of the resultant displacement, you must algebraically add the sum of their seperate displacements.
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22:10:42 ** 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 --> ok
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22:12:11 **** 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 --> Angle of incidence is an angle which is perpendicular to the surface. it reflects and equal angle on the other side of the perpindicular.
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22:12:16 ** 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 --> ok
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~Jͨ assignment #020 020. `Query 10 Physics II 07-16-2007