Sound Waves and Their Behavior

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Sound Waves and Their Behavior — Free MYP4 Physics Practice Questions

1QuestionApplications Sonar Ultrasound and Musical InstrumentsConcept Practice

2 marks~3 minCriterion A

Ultrasound scanners used in hospitals emit sound waves at frequencies above 20 000 Hz to produce images of internal structures.

State one medical application of ultrasound technology. [1]

Explain one limitation that reduces the effectiveness of ultrasound imaging in a specific clinical situation. [1]

Solutions

2QuestionApplications Sonar Ultrasound and Musical InstrumentsAssessment Practice

3 marks~5 minCriterion A

An ultrasound pulse is emitted at

t = 0\ \mu\text{s}

and travels through layers of skin, fat, and muscle. The first reflected pulse returns at

t = 13\ \mu\text{s}

with an amplitude equal to

80\%

of the emitted pulse. The second reflected pulse returns at

t = 26\ \mu\text{s}

with an amplitude equal to

40\%

of the emitted pulse.

State one mechanism by which the ultrasound pulse loses energy as it travels through biological tissue. [1]

Explain how acoustic impedance mismatch at a tissue boundary determines the amplitude of a reflected pulse. [1]

Using the data provided, explain why the second reflected pulse has a smaller amplitude than the first. [1]

Solutions

3QuestionApplications Sonar Ultrasound and Musical InstrumentsAssessment Practice

4 marks~6 minCriterion B

The table below shows string lengths and fundamental frequencies for four orchestral string instruments.

Instrument	Violin	Viola	Cello	Double Bass
String length (m)	0.33	0.43	0.70	1.10
Fundamental frequency (Hz)	196	150	92	59

Deduce the fundamental frequency of a string instrument with a string length of 0.55 m. Support your answer with a calculation using the pattern in the data. [2]

Justify the relationship between string length and fundamental frequency using the wave equation

v = f\lambda

and the condition for a standing wave on a string fixed at both ends. [2]

Solutions

4QuestionSpeed of Sound in Solids Liquids and GasesAssessment Practice

5 marks~8 minCriterion C

The kinetic-molecular model predicts the speed of sound in a medium using

v = \sqrt{\frac{B}{\rho}}

where

B

is the bulk modulus and

\rho

is the density. Measured and theoretical speeds of sound at 20°C are given below.

Medium	Measured speed (m/s)	Theoretical speed (m/s)
Air	343	330
Water	1482	1500
Steel	5960	6100

Percentage discrepancy is defined as

\text{Percentage discrepancy} = \frac{|\text{Measured} - \text{Theoretical}|}{\text{Theoretical}} \times 100

Calculate the percentage discrepancy for each medium. [3]

Deduce which state of matter the kinetic-molecular model describes most accurately, using your results from (a). [1]

Evaluate the overall validity of the kinetic-molecular model for predicting the speed of sound across all three states of matter. [1]

Solutions

5QuestionApplications Sonar Ultrasound and Musical InstrumentsAssessment Practice

6 marks~9 minCriterion D

A medical technician uses ultrasound to examine two structures: a liver tumour approximately 12 cm below the skin and a thyroid nodule approximately 2 cm below the skin. Two probes are available: one at 3.5 MHz and one at 7.5 MHz. The speed of ultrasound in human tissue is

1540 \, \text{m/s}

Calculate the wavelength of the 3.5 MHz ultrasound in tissue. [1]

The 7.5 MHz probe produces a wavelength of

2.05 \times 10^{-4}

m in tissue. Deduce how this shorter wavelength affects the minimum size of structure that can be detected, and state one consequence for imaging deep tissue. [2]

Evaluate which probe is more appropriate for each examination. In your response, analyse the trade-off between resolution and penetration depth, and discuss how the assumption of uniform tissue density may limit the accuracy of either probe. [3]

Solutions

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