Review &The hardest MC questions in media, waves, A guide for the perplexed

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1 Review &The hardest MC questions in media, waves, A guide for the perplexed

2 Grades online pp. I have been to the Grades online and A. Mine are up-to-date B. The quizzes are not up-to-date. C. My labs are not up-to-date D. My HW is not up-to-date E. I have not been to grades online. Quiz 9: 3 clicker # TO BE assigned to a student

3 Wed noon Today: 1. More on standing waves in tubes. 1. Why real waves in pipes are not same as the math. 2. More on music and Fourier 1. The cheat to give us the 12-tone scale. 2. Instruments and square waves. Remember: the online schedule has precedence.

4 Thinking about standing waves in pipes

5 Try out my piece of pipe f=nv/(2l) ; n = 1 f=343 m/s /(2*0.228 m) =752 Hz But correct pitch is 720 Hz, How to account? Velocity of sound? Temperature? v= 331 [1+T/273]m/s Length? L = v/(2f) = ½*343 m/s/720 Hz =0.238 m Antinodes extend out from each end?

6 Why do they show the sine curve with nodes at the tubes end? Our book shows nodes in the middle and AN at the ends? Suppose we have an even fatter tube? pp. A.The tone is higher B.The tone is lower

7 What note is 720 Hz? Look at Chapter Summaries. Start with A 720/440 = Between F and F# What if it were much lower than 440Hz? E.g. 360 or 262Hz? AGAIN Between F and F# or C

8 Circle of fifths does white notes F G A B C D E

9 What would happen if velocity went way up? n = 1 n = 2 n = 3 f= nv/(2l)

10 Helium velocity of sound. 930 m/s v sound air about 330 m/s

12 Frequency C C G C E G CCGCEG

13 Fourier Analysis

14 Organ Pipes: pitch =v/(2l) Middle C= 262 Hz 2 octaves down is f = 262/2 2 = 65 Hz L =½343m/s/65/s= 2.6 m 8 ft 3 octave above C Pipe is 8/2 5 = 3 in.

17 How hot should the earth be? W/m 2. This is the solar constant. Fourier is credited with the discovery in 1824 that gases in the atmosphere might increase the surface temperature of the Earth [1]. This was the effect that would later be called the greenhouse effect. He established the concept of planetary energy balance - that planets obtain energy from a number of sources that cause temperature increase. Planets also lose energy by infrared radiation (that Fourier called "chaleur obscure" or "dark heat") with the rate increasing with temperature. A balance is reached between heat gain and heat loss; the atmosphere shifts the balance toward the higher surface temperatures by slowing the heat loss. AIP:

18 Where do the exam questions come from? (BRING Chapter Summaries) Sources of questions: 1. Questions which are suggested by classroom Discussions & Demos. This includes quizzes and vocabulary/distinctions stressed/mentioned in class. 2. Quick quizzes from the chapters 3. Questions in the back of the chapters 4. Labs 5. HW variations (though we can t ask as many of the harder/longer problems.) 6. HW problems from the book 7. Imagination (up to ½ ).

19 Ambiguities and questions How long between nodes in lab 3 and is this the same as the 2-speaker Demo? If v of sound goes up what happens to a violin, what about a flute? What is human voice more like? Violin or flute? (Helium) understanding What music facts are needed to know? (CS) Octaves: Two tones are an octave apart if one pitch has twice the frequency of the other. In written music there are 12 intervals in each octave, with the ratio between successive intervals equal to 2 1/12 = Geometric series.

20 How much is the cheat to get 12 tones? 440 is A. Up a 5 th is E. E should be 660 Hz. On equal tempered scale it is Hz. Can you hear it? On line.

21 Middle C is 262 HZ What is the frequency of the next higher C? Special instructions for numerical problems: READ THIS, PLEASE. If a number is requested and MC options are not provided, fill in the bubble corresponding to the left-most digit of the number you compute when the number is expressed in proper scientific notation. Keep at least three digits. You will not use zero unless the number is exactly zero. Thus will be 7.

22 Middle C is 262 HZ What is the frequency of the two octaves above middle C? Special instructions for numerical problems: READ THIS, PLEASE. If a number is requested and MC options are not provided, fill in the bubble corresponding to the left-most digit of the number you compute when the number is expressed in proper scientific notation. Keep at least three digits. You will not use zero unless the number is exactly zero.

23 Exam 1: Buoyancy A block of wood with a steel weight attached floats in a bowl of water. The weight detaches, sinks, and comes to rest on the bottom. When this happens, the water level in the bowl (a) goes up. (b) remains unchanged. c) goes down Item disc: Fair (0.31) Item difficulty: Difficult (0.66)

24 Waves Write the equation of a wave, traveling along the +x axis with an amplitude of.02 m, a frequency of 440 Hz, and a speed of 330 m/sec. Item discrimination: Fair (0.38) Item difficulty: Difficult (0.68) a. y =.02 sin [880π( x/330 t)] b. y =.02 cos [880π x/ t] c. y =.02 sin [880π(x/330 + t)] d. y =.02 sin [2π(x/ t)] e. y =.02 cos [2π(x/ t)]

25 How much louder is the intensity of sound at a rock concert in comparison with that of a whisper, if the two intensity levels (in db) are 110 and 30, respectively? Express the loudness as 10 to an exponent. Pencil in the first digit of the magnitude of that exponent on the bubble sheet. (That is, an exponent of 2.3 would be 2). Item discrimination: Good (0.46) Item difficulty: Easy (0.61) 8

26 Continuing the previous question, associated with the louder noise is a larger pressure amplitude. Express the ratio of the large amplitude to the smaller amplitude as 10 to an exponent. Pencil in the first digit of the exponent on the bubble sheet. 4 Item discrimination: Fair (0.38) Item difficulty: Very Difficult (0.22) (i.e., an exponent of 2.5 would be 2.)

27 If we want to increase the # of loops in the standing waves we should: beaker or produced in lab 2, 1. Remove water from the 2. Add H2O to the beaker Hint this is the schematic of the apparatus:

28 Standing Waves Two harmonic waves traveling in opposite directions interfere to produce a standing wave described by y = 2 sin (πx) cos (3πt) where x is in m and t is in s. What is the distance (in m) between the first two antinodes? A. 8 B. 2 C. 4 D. 1 (lambda/2) E. 0.5 Item discrimination: Good (0.44) Item difficulty: Difficult (0.60)

30 Two speakers emit sound waves with identical frequency. The power emitted from each speaker is the same and is held constant. The sound waves interfere in a region of space. Some locations experience destructive interference resulting in no sound. Other regions experience constructive interference. A. Energy is not conserved because of the missing energy in the destructive regions. B. The constructive regions have approximately double the intensity from one speaker alone and energy is conserved. C. The constructive regions have approximately four times the intensity from one speaker alone. D. Energy is drawn into and stored in one of the speakers.

31 Header PHYSICS 123(1) Exam 1 Winter 08 A must - CID# 1. Put your cid number each place it is requested. It is a good idea to it on each sheet. 2. The first part of the exam is multiple choice/ leftmost digit. Equal pts/ problem. Choose the best answer. Special instructions for numerical problems: READ THIS, PLEASE. READ THIS, PLEASE. If a number is requested and MC options are not provided, fill in the bubble corresponding to the left-most digit (LMD) of the number you compute when the number is expressed in proper scientific notation. Keep at least three digits. You will not use zero unless the number is exactly zero. Thus will be 7. If I ask for second leftmost digit (SLMD) the answer will be 8. If units are not specified use SI. 3. After that comes several homework-style problems which will be graded by hand. Partial credit will be given so please answer these problems clearly and label your work carefully. Also see that your answers and scratch work are attached to your test as you leave the testing center. Make sure to put your work in order. Staple it to the cover sheet well. You may call me at , or home You can use: a calculator of any kind, scratch paper, the Chapter Summaries. No time limit. Good luck Ask the TC for a loaner copy of the CS if you did not bring yours. Remember to return it after the exam. NO OTHER BOOKS OR NOTES. YOU may NOT DISCUSS THIS EXAM WITH OTHERS

Exam 4. Today last regular day Tomorrow (Saturday) is the late day Your study guide is the homework!

Exam 4. Today last regular day Tomorrow (Saturday) is the late day Your study guide is the homework! Exam 4 Today last regular day Tomorrow (Saturday) is the late day Your study guide is the homework! Final Exam All Finals week in the RB Same format, same rules as midterms, but no free response - one