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.
- 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]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.
- [1] diameter/d is the independent variable and frequency/f is the dependent variable or vary d and measure f
- [1] keep L constant or length (of tube) constant
- [1] labelled diagram of workable experiment including: tube supported • (loud)speaker positioned in line with the tube • (loud)speaker labelled
- [1] labelled microphone, positioned outside tube in line with tube, connected to labelled oscilloscope or correct circuit symbol
- [1] adjust/change frequency until maximum amplitude detected
- [1] use calipers to measure d
- [1] plot a graph of 1/f against d or d against 1/f (Do not accept logarithmic graphs.)
- [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
- [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
- [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
- [1] (D2) use a rule to measure L
- [1] (D3) increase frequency from a low frequency to the first maximum amplitude
- [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
- [1] (D5) method to determine period from oscilloscope, e.g. no. of divisions × time-base
- [1] (D6) for frequency/time period determined by oscilloscope, f = 1 / T
- [1] (D7) repeat measurements of d and average in different directions/positions or along the tube
- [1] (D8) perform experiment in a quiet room
- [1] (D9) signal generator connected to (loud)speaker in diagram
- [1] (D10) relationship valid if a straight line produced (Do not accept through the origin.)
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