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A-LevelPhysicsWaves9702/51 · Oct/Nov 2021 · Q115 Marks

A student investigates stationary sound waves in cylindrical tubes. Fig. 1.1 shows a stationary wave pattern in a tube which is open at both ends. L d cylindrical tube Fig. 1.1 The tube has length L and diameter d. The frequency of the sound for the stationary wave pattern shown is f. There are a number of different tubes available. It is suggested that the relationship between f and d is V = 2L + kd f where v is the speed of sound in air and k is a constant. Design a laboratory experiment to test the relationship between f and d. Explain how your results could be used to determine values for k and v. You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to: • the procedure to be followed • the measurements to be taken • the control of variables • the analysis of the data • any safety precautions to be taken.

  1. A student investigates stationary sound waves in cylindrical tubes. Fig. 1.1 shows a stationary wave pattern in a tube which is open at both ends. L d cylindrical tube Fig. 1.1 The tube has length L and diameter d. The frequency of the sound for the stationary wave pattern shown is f. There are a number of different tubes available. It is suggested that the relationship between f and d is V = 2L + kd f where v is the speed of sound in air and k is a constant. Design a laboratory experiment to test the relationship between f and d. Explain how your results could be used to determine values for k and v. You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to: • the procedure to be followed • the measurements to be taken • the control of variables • the analysis of the data • any safety precautions to be taken.[15]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

  1. [1] diameter/d is the independent variable and frequency/f is the dependent variable or vary d and measure f
  2. [1] keep L constant or length (of tube) constant
  3. [1] labelled diagram of workable experiment including: tube supported • (loud)speaker positioned in line with the tube • (loud)speaker labelled
  4. [1] labelled microphone, positioned outside tube in line with tube, connected to labelled oscilloscope or correct circuit symbol
  5. [1] adjust/change frequency until maximum amplitude detected
  6. [1] use calipers to measure d
  7. [1] plot a graph of 1/f against d or d against 1/f (Do not accept logarithmic graphs.)
  8. [1] for 1/f against d: v = 2L / y-intercept or v = gradient × k or v = gradient × 2L / y-intercept OR for d against 1/f: v = gradient × k or v = 2L / y-intercept
  9. [1] for 1/f against d: k = gradient × v or k = gradient × 2L / y-intercept OR for d against 1/f: k = -2L / y-intercept
  10. [1] (D1) wear ear defenders (to prevent damage to hearing/to avoid loud sounds) or use a low volume to prevent damage to hearing/to avoid loud sounds
  11. [1] (D2) use a rule to measure L
  12. [1] (D3) increase frequency from a low frequency to the first maximum amplitude
  13. [1] (D4) method to determine f at maximum amplitude, e.g. increase frequency to f, then continue increasing frequency, and then decrease frequency until value of f determined
  14. [1] (D5) method to determine period from oscilloscope, e.g. no. of divisions × time-base
  15. [1] (D6) for frequency/time period determined by oscilloscope, f = 1 / T
  16. [1] (D7) repeat measurements of d and average in different directions/positions or along the tube
  17. [1] (D8) perform experiment in a quiet room
  18. [1] (D9) signal generator connected to (loud)speaker in diagram
  19. [1] (D10) relationship valid if a straight line produced (Do not accept through the origin.)

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About this question

Topic
Waves, A-Level Physics (syllabus 9702). Structured question, 15 marks.
Source
A-Level Physics, Oct/Nov 2021 Paper 5 Variant 1, question 1.

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