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IB · C · multiple choice

Wave behaviour · Question 3

Wave behaviour · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
demanding
Marks
1
Topics
1
Answer
Complete
A pipe of length 0.85 m, closed at one end and open at the otherclosed endopen endair, speed of sound 340 m s⁻¹L = 0.85 m
Figure 1Side view of a horizontal pipe drawn as a long rectangle lying on its side. Its left-hand end is sealed by a wall drawn with hatching behind it and labelled 'closed end'; its right-hand end has no wall drawn across it and is labelled 'open end'. The air column inside carries the note 'air, speed of sound 340 m s⁻¹', and a dimension line beneath the pipe, with a tick at each end, marks its length as L = 0.85 m from the closed end to the open end.
multiple choice1 mark

A pipe of length 0.85 m is closed at one end and open at the other. The speed of sound in air is 340 m s⁻¹. What is the frequency of the fundamental note?

  1. A

    100 Hz

  2. B

    200 Hz

  3. C

    400 Hz

  4. D

    800 Hz

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Answer overviewCorrect answer: A — 100 Hz
01

Answer and reasoning

1 mark
How to approach it

Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.

  1. 1

    The correct choice is A: 100 Hz

  2. 2

    B is the answer for a pipe open at both ends. A closed pipe has a node at the closed end and an antinode at the open end, so the fundamental fits only a quarter of a wavelength into its length: λ = 4L = 3.4 m.

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