O-LevelPhysicsWaves5054/21 · Oct/Nov 2024 · Q59 Marks

Ultrasound is a longitudinal wave which cannot be heard by humans as the frequency of ultrasound is too high.

(a)Ultrasound waves cannot travel in a vacuum. Explain why.[2]
(b)Describe how a longitudinal wave differs from a transverse wave.[2]
(c)An ultrasound transmitter used for a medical scan produces an ultrasound wave of frequency 8.4 MHz. In soft human tissue, ultrasound travels at 1500m/s.
(c)(i)Calculate the wavelength of this ultrasound wave in soft human tissue. wavelength = ................................................................. m [3][3]
(c)(ii)The ultrasound wave passes from the soft tissue into bone where the speed of the ultrasound wave is greater than 1500 m/s. State what happens to the frequency and to the wavelength of the ultrasound wave as it passes into the bone. frequency .......................................................................................................................................................................................... wavelength ...................................................................................................................................................................................... [2][2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

[B1] ultrasound / sound / it is transmitted by vibrating matter / particles
[B1] no matter / particles in a vacuum / no medium
[B1] (in a longitudinal wave,) vibration (of particles) is parallel to the propagation direction
[B1] in a transverse wave, vibration (of particles) is perpendicular to the propagation direction
[C1] (λ =) v / f or 1500 / 8.4 × 10⁶
[C1] 1.8 x 10N
[A1] 1.8 × 10⁻⁴ (m)
[B1] frequency: does not change
[B1] wavelength: increases

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