DP Physics (last assessment 2024)

Question 18N.2.HL.TZ0.b

Date	November 2018	Marks available	[Maximum mark: 4]	Reference code	18N.2.HL.TZ0.b
Level	HL	Paper	2	Time zone	TZ0
Command term	Determine, State	Question number	b	Adapted from	N/A

[Maximum mark: 4]

18N.2.HL.TZ0.b

A pipe is open at both ends. A first-harmonic standing wave is set up in the pipe. The diagram shows the variation of displacement of air molecules in the pipe with distance along the pipe at time t = 0. The frequency of the first harmonic is f.

The speed of sound c for longitudinal waves in air is given by

$c = \sqrt {\frac{K}{\rho }}$

where ρ is the density of the air and K is a constant.

A student measures f to be 120 Hz when the length of the pipe is 1.4 m. The density of the air in the pipe is 1.3 kg m^–3. Determine the value of K for air. State your answer with the appropriate fundamental (SI) unit.

[4]

Markscheme

wavelength = 2 × 1.4 «= 2.8 m» ✔

c = «f λ =» 120 × 2.8 «= 340 m s⁻¹» ✔

K = «ρc² = 1.3 × 340² =» 1.5 × 10⁵ ✔

kg m^–1s^–2 ✔

Syllabus sections

Core

Core » Topic 4: Waves » 4.2 – Travelling waves

Core » Topic 1: Measurements and uncertainties » 1.1 – Measurements in physics

Core » Topic 1: Measurements and uncertainties

Core » Topic 4: Waves

Question 18N.2.HL.TZ0.b

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