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Unformatted text preview: pokharel (pp7242) Sound and Light ReTest walther (16180) 1 This print-out should have 32 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Explain how you can lower the pitch of a tone on a guitar by altering (a) the length of the string, (b) the tension of the string, or (c) the thickness or the mass of the string. 1. shorter, tighter, and lighter 2. shorter, looser, and more massive 3. longer, tighter, and more massive 4. longer, looser, and lighter 5. longer, looser, and more massive correct Explanation: A low pitch will be produced when a gui- tar string is (a) lengthened, (b) loosened so that tension is reduced, and (c) made more massive, usually by winding wire around the string. Thats why bass strings are thick. 002 10.0 points A pulse moves on a string at 1 m/s, traveling to the right. At point A , the string is tightly clamped and cannot move. 1 m/s 1 m A Which of the following shows how the string would look soon after 2 seconds? 1. A 2. A 3. A 4. A 5. A 6. A 7. A correct 8. A Explanation: The pulse travels to the right and is re- flected back from the fixed point. The wave cannot propagate to the right beyond the point A . Reflected pulses from fixed end points are inverted. 003 10.0 points One end of a horizontal string is fixed to a wall. A transverse wave pulse in the form of a crest is generated at the other end and moves toward the wall, as shown. Consider the pulse after it has been reflected by the wall. v What is/are correct concerning the reflected pulse ? A) The reflected pulse forms a crest. pokharel (pp7242) Sound and Light ReTest walther (16180) 2 B) The reflected pulse has a greater ampli- tude than that of the incident pulse. C) The reflected pulse has a greater speed than that of the incident pulse. D) The reflected pulse forms a valley. 1. C only 2. A and B only 3. D only correct 4. B only 5. A only 6. A and C only 7. B and C only 8. A, B and D only 9. A and D only 10. B and D only Explanation: The speed of the pulse is determined by the tension of the string and the mass per unit length, and is the same for the incident and reflected pulses. The reflected pulse cannot have an ampli- tude greater than that of the incident pulse, since no energy is added to the pulse at the wall. There is a phase shift of at the wall, because the end fixed at the wall cannot move, so the reflected pulse is on the opposite side of the string from the incident pulse, forming a valley. Incident crests reflect as valleys, and vice versa. 004 10.0 points Consider the sinusoidal wave pictured in the figure 6 m 1 m y x O What equation describes the wave?...
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This note was uploaded on 06/07/2010 for the course PHYSICS 58930 taught by Professor Kleinman during the Fall '09 term at University of Texas at Austin.
- Fall '09