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lecture31 - midterm2 re-visited

# lecture31 - midterm2 re-visited - What you will be...

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Unformatted text preview: What you will be able to do a/er today … Explain … Calculate … •  what went wrong on Midterm 2 •  review some problems – try them like NEW Apply … •  what you studied for the midterm Midterm 2: secKon 102 class average 30.4 (67.6%) 50 45 number of students 40 35 30 25 20 15 10 5 0 1 2 3 4 5 6 7 Your BETTER midterm mark will count for 10%, the other one for 5 % of your midterm mark QuesKon part, please marks for each circle you A car, which is sounding its horn, speeds up towards you. Which of MC1 A car which is s the following does not change? ounding its horn, speeds up toward circle your answers. change? (A)  frequency (B) sound speed (C) wavelength (D) intensity up towardsrequency folrowing does aJ f you. which of the bl sound speednot c) wavelengtà A spring mA spring has mass M and spring constant k and MC2 ass system ass system, has_mass M and.spring const m oscillates amplitude A avelengtà with d) intensity . If the spring constant is doubled Ifthe spring constant is d to 2k, but the mass and the total oubled remain tbutstné mais and energy to 2lç he ame, new ampìitude is: pring then the new amplitude is: with amplitude A. constant k and oscillates mais and total energy remain the sam| then the a)A b) 2A c) A/2 /2 Mc3 A long string is constructed by joining 2 shorter str e) r/ãe ü same but string I has 4 times the mass/length MC2 A spring mass system, has_mass M and.spring constant k and Ifthe spring constant is doubled to 2lç but tné mais and total ene new ampìitude is: QuesKon a)A b) 2A A long string is constructed by joining 2 shorter c) A/2 The strings. ü tension in the strings is the same but string I has 4 Kmes the mass/ Mc3 A long string i cWhen a sinusoidal wave passes strings. The length of string II (μI=4μs). onstructed by joining 2 shorterfrom II same s ut string sKng I to btring II: I has 4 times the mass/length of string II, (trr=4 pl) passes from string I to string II. a) the frequency decreases by a factor of 4 b) the frequency decreases by a factor of2 cJ the wavelength decreases by a factor of 4 d) the wavelength decreases by a facßr of 2 eJ the wavelength increases by a factor of 2 fJ the wavelength increases by a factor of 4 worksheet: midterm 2 review Question 4 (10 marks) The left graph shows a havelling wave D(x,t) as a function of time forx = 0. The right graph shows the same wave as a function of x for a particular time tl . D has units cm, x has units of meters and t has units ofseconds., The wave is moving from right to left (i.e. in the direction ofdecreasing x). History Graph Snapshot graph I D(r-.tl) 0.5 Ð(0,0 -. ,1 . 0 oi5 -0.5 I -1 a) What is the wavelength, frequency and amplitude of this wave? )F È b) Write a¡ equation for this wave and determine its phase constant. Clearly show how you determined the phase constant - worksheet: midterm 2 review Question 5 (Smarks) Ir +( 720m You are standing against a wall, 120 m from two speakers, The speakers are separated by 3.0 m. The two speakers are in phase and emit the same frequency, Assume, the speed of sound is 340 m/s When you stand on the centre line and then walk along the wall, you notice that the sound first goes quiet when you are directly in front ofone ofthe speakers, position marked with an x. What is the frequency ofthe sound? last worksheet A laser beam (l = 500 nm) is incident on a graKng with two slits separated by a distance, d, of 1.0 mm with a screen placed a distance, L, 1.0 m away. The 2 slits are so small that the light waves coming out of them can be assumed to be point sources. Since d<<L, we can assume both rays (r1 and r2) to be parallel at an angle θ. (a) are the two sources in phase? EXPLAIN in a sentence (b) Is there a path length diﬀerence? EXPLAIN in a sentence What is this arrow indicating ? (c) Try to write an equaKon for determining the height posiKon (y) of each construcKve maxima (bright ‘fringe’). Young s Double Slit Experiment •  Interference pattern: waves in phase (constructive, bright) or out of phase (destructive, dark). •  Phase difference due to path length difference Length (slit1 - screen) ≠ Length(slit2 - screen). •  Constructive: path difference ΔL= m·λ (m = 0,1,2,3...). •  Destructive: path difference ΔL = m·λ/2 •  Angle of red and blue ray almost the same, if d << L θ θ ΔL = d sin θ L 8 Young s Double-Slit Experiment •  Constructive (bright fringe) if d sin θ = mλ •  Destructive (dark fringe) if 1 ȹ ȹ d sin θ = ȹ m + ȹλ 2 Ⱥ ȹ •  Two bright fringes separated by Δm =1 (HeNe laser, typical distances): Δy = L tan( Δθ ) ≈ L sin( Δθ ) = L λ d = 2.0m θ θ ΔL L 632.8 nm = 1.3 mm 1.0 mm 4 3 2 1 0 1 2 3 4 9 worksheet Coherent light of frequency 6.32 x 1014 Hz passes through two thin slits and falls on a screen 85.0 cm away. You observe that the third bright fringe occurs at +/- 3.11 cm on either side of the central bright fringe. (a)  How far apart are the two slits? (b)  At what distance from the central bright fringe will the third dark fringe occur? 10 worksheet 1= Problem 5: 3 , to?nfr, 6.ge*to'1t'[z , Q74 nn Coherentlightoft,[email protected] 85.O cm away. You observe that the third bright fringe occurs at +/- 3.LL cm on either side of the central bright fringe. (a) How far apart are the two slits? (b) At what distance from the central bright fringe will the third dark fringe occur? [t) dP;*- e' -fr'- rztrS, eG) '-'oÀ (z) t .s 3. It /þ^ er,,t t{c,^ -'(+) .F 3ie. (o t*,t^Å ols,;9ê) = 3À Problem 6:, d.. ?T ï, - 3t,1pm R = 7Çc+o, Feæ,-e The microwaves in a certain microwave oven have a wavelength of L2.2 cm. (a) How wide must this oven be so that it will contain six nodal planes of the microwave disturbance (including the nodal plane at each walls) along its width in the standing wave pattern? = 2,lnø worksheet: challenge Red light with wavelength 700 nm is passed through a twoslit apparatus. At the same time, monochromatic visible light with another wavelength passes through the same apparatus. As a result, most of the pattern that appears on the screen is a mixture of two colors. However, the center of the third bright fringe (m = 3) of the red light appears pure red, with none of the other color. (a)  What are the possible wavelengths of the second type of visible light? (b)  Do you need to know the slit spacing to answer this question? Why or why not? 12 worksheet challenge problem \? t- N --' l"*=--'L ? È'...''.1 õ r f VisïLt¿ lykl sp".+"r,,*o= te. flW"r^*ffi#,çs^ {¿4"9*) Problem 5: Red light with wavelength ,OOåff', passed through a two-slit apparatus. At the same t¡me, monochromatic visible light with another wavelength passes through the same apparatus. As a result, most of the pattern that appears.on the screen ¡s a mixture of two colors; however, the center of the third bright fringe (m = 3) of the red lighl appears pure red, with none of the other color. What are the possìble wavelengths of the second type of visible light? Do you need to know the slit spacing to answer this question? Why or why not? 5o ¿ha g¿,i^ù .þ^¿l of +Às {Stt *u&ì'bø tu*\$þfu @rfu¿¡eh* a'f tk* ct'¡*3 eø"t\$}"'valr'*e F*¿l .ê\$hd L L K "3*3.={,*t)à}n}o Y.^" ea,t¿¿}-{t* a'¿J el sivr¿e l.r¡e-q ¿r\** .'-\ - \ :-:-!::-i b:il ,ttr aê e?",,aø+o. orr 4xå ä dL -l't.t J¿,v\(, ga.r"w*ukis Problem 6: ê", L*fin løì¡¡.s sË; {5J ¡ lb(,nu Aøi-l,we¿ 3"3 . {4"e- 5,7 r. 6ooar, 61 5,5Å l :S+n, û,tV rte};f (^,¡ .So.) a.SÀ; &tu.^rnn \rÀfë(\i"ø¿ lgL{ )Lt{ow t¡ur* 13 ...
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