Lecture 28 Announcements 1 Tutorial lab info it will be open during reading days and finals but the TAs have their own exams to study for and take so staffing may vary significantly from the regular schedule 2 Final exam a Take in Testing Center anytime during finals week See Testing Center website for their exact schedule b Will have 40 problems c 10 problems on new stuff rest is cumulative d Average time should be 2 2 5 hours i 4 hr time limit e Last year s median 75 this year s exam is a little harder I m shooting for 72 73 i I ll curve it up to 70 if it ends up being below that f No calculators no notecards g First page of exam has been posted to class website that tells you which formulas will be given on exam h What to study roughly in order of importance i Midterm exams ii Homework all of them but especially the last three assignments iii Class notes iv Warmup quizzes Colton Lecture 28 12 11 08 pg 1 v Last year s final vi Textbook 3 Two TA led final exam reviews room still TBA a Thurs 7 9 pm b Fri 1 3 pm 4 Deadlines a All extra credit must be turned in to your regular homework boxes by midnight tonight b Instructor course ratings must be done by Sat Dec 13 http studentratings byu edu c All late computer homework must be done by midnight Fri Dec 19 last day of finals Colton Lecture 28 12 11 08 pg 2 Formulas Review Chap 13 14 Things which you might consider to be formulas but I don t really so I won t give them to you on exam Definitions and Fundamental Laws Final exam you will be expected to know these on your own 1 2 f 2 f T T Wave speed v f Intensity I P A What A and stand for in the equation for a sinusoidal wave i e x Acos t How to solve for I in the decibel formula How to choose signs in Doppler formula n New stuff but not quite as basic Final exam I will give you these but maybe without the tags m k spring m T 2 k L g pendulum L T 2 g T How to use e g L 2 formula to figure out frequency of a harmonic I m sure there are more Y B wave speed v m L v v vair 343 m s unless otherwise specified Asphere 4 r2 I decibels 10 log I 0 I0 10 12 W m2 v v O Doppler f f v v S n standing waves L 2 n 1 2 3 L Colton Lecture 28 12 11 08 pg 3 n n 1 3 5 4 Colton Lecture 28 12 11 08 pg 4 Review of important concepts Chap 13 14 I b Decibel scale sound 10 log I 1 Sinusoidal Oscillations Asin t or Acos t a Amplitude b Period vs frequency vs angular frequency 1 2 i f T 2 f T c Simple harmonic motion k i spring m 0 I0 10 12 W m2 i 10 to dB number 10 to the intensity v v0 f f c Doppler effect v vS i If lady observer is moving towards baker 1 numerator because freq increases ii If baker source is moving towards lady 1 denominator because freq increases iii If moving away use opposite sign g ii pendulum L 1 When does this hold true 2 Waves oscillations that transport energy a Often sinusoidal in space and in time b Longitudinal vs transverse c Reflections when does an upward pulse reflect off downward d Superposition interference e Speed wavelength frequency v f f Equations for wave speed in different materials i sqrt force like quantity mass like quantity 3 Sound waves a Intensity of a wave I P A i Spherical waves A 4 r2 Colton Lecture 28 12 11 08 pg 5 Some HW problems missed by many HW 20 1 A 5 56 g object is suspended from a cylindrical sample of collagen 3 58 cm long and 2 12 mm in diameter If the object vibrates up and down with a frequency of 30 3 Hz with is the Young s modulus of the collagen 4 Interference superposition of waves a Constructive destructive interference i Waves off by vs waves off by 2 b Standing waves i Vocabulary nodes vs antinodes ii Closed closed or open open 1 L 1 2 2 2 3 2 from pictures n 2 Summary L 2 n 1 2 3 iii Open closed 1 L 1 4 3 4 5 4 from pictures n 2 Summary L 4 n 1 3 5 iv Freq of nth harmonic wavespeed of nth harmonic c Beats fbeat f1 f2 Colton Lecture 28 12 11 08 pg 6 HW 21 4 A stereo speaker emits sound waves with a power output of 26 6 W a Find the intensity 10 5 m from the source Assume that the sound is emitted uniformly in all directions from the speaker b Find the intensity level in decibels at this distance c At what distance would you experience the sound at the threshold of pain 120 dB Answers 0 0192 W m2 102 8 dB 1 45 m Answer 2 04E06 Colton Lecture 28 12 11 08 pg 7 Colton Lecture 28 12 11 08 pg 8 HW 22 2 A pair of speakers separated by 0 76 m are driven by the same oscillator at a frequency of 690 Hz An observer originally positioned at one of the speakers begins to walk along a line perpendicular to the line joining the two speakers a How far must the observer walk before reaching a relative maximum in intensity b How far will the observer be from the speaker when the first relative minimum is detected in the intensity Take the speed of sound to be 345 m s HW 22 5 Two identical mandolin strings under 205 6 N of tension are sounding tones with fundamental frequencies of 523 Hz The peg of one string slips slightly and the tension in it drops to 196 7 N How many beats per second are heard Answers 0 33 m 1 03 m Answer 11 4 Colton Lecture 28 12 11 08 pg 9 Some clicker quizzes Clicker quiz 1 You hear a 70 dB sound After a while the sound has its intensity increased by a factor of 100 The new decibellevel will be dB A 50 B 60 C 80 D 90 E 100 Clicker quiz 2 When people stand up and sit down in a stadium to perform the wave this is an example of what kind of wave A Longitudinal B Circular C Simple Harmonic D Transverse Clicker quiz 3 A mass on a spring oscillates with a certain frequency The mass is removed and a mass weighing 9 times as much is put on the same spring What is the ratio of the new frequency to the old …