AS 91523 · 2024 paper · the pan flute
Question 1(a) Achieved
Practises Standing waves & resonance
A pan flute is a set of pipes of different lengths bound together, each CLOSED at one end and open at the other. Sound is made by blowing across the open ends. Jane's shortest pipe is 8.50 cm long and her longest is 17.5 cm. The speed of sound in air is 343 m s⁻¹.
| v sound | 343 m s⁻¹ |
|---|---|
| shortest pipe | 8.50 cm |
| longest pipe | 17.5 cm |
Draw the third harmonic that a pan flute pipe can produce, and label the nodes (N) and antinodes (A).
The 2024 paper, page 2 ↗ Marking schedule, page 1 ↗
See it move: Standing waves: string, open pipe, closed pipe
Work it out
Try it on paper first. Stuck? Take one hint at a time.
-
1 What must happen at each end of the pipe?
The closed end is a node: the air against the wall cannot move. The open end is an antinode: the air there moves most freely. -
2 Which harmonics can a pipe closed at one end make, and how much of a wavelength does the third fit in?
Only odd ones, because the pipe has to hold an odd number of quarter-wavelengths. The first holds one quarter, from the node to the antinode. The third holds three quarters: L = 3λ/4. -
3 Place the nodes and antinodes along the pipe.
From the closed end: N, then A a third of the way along, then N two-thirds of the way along, then A at the open end. Two nodes and two antinodes, and the curve reaches both ends of the pipe.
What the marker wanted
- Achieved The right shape, with at least one node and one antinode labelled correctly. The wave has to reach the end of the pipe.
In our words, from NZQA’s 2024 marking schedule.
✕Common mistake
A wave that stops short of the open end, or loops of different sizes. NZQA’s 2024 report lists both among answers that did not reach Achieved, and the schedule notes that the wave must reach the end of the pipe.How did it go?
Got it moves it further out. Review brings it back tomorrow.