Uses of Ultrasound
Revise Uses of Ultrasound for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: ultrasound is sound above 20 000 Hz, and its reflections are used in medical imaging and to measure distances.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
This is a Higher tier only topic, so there's no Foundation paper — only the Higher worksheet and mark scheme below.
Topic overview
Ultrasound waves have a frequency higher than the upper limit of human hearing, above 20 000 Hz. This is a Triple-only and Higher-only topic.
When an ultrasound wave meets a boundary between two different media, part of the wave is reflected back. The time taken for the reflections to reach a detector can be used to determine how far away the boundary is.
The distance is calculated using distance = speed × time, then halved, because the wave travels to the boundary and back again. Forgetting to halve is the most frequent error. Uses include medical imaging such as pre-natal scanning, and industrial imaging to detect flaws inside objects.
Revision notes
What ultrasound is
Ultrasound waves have a frequency above 20 000 Hz, higher than the upper limit of human hearing.
They behave like other sound waves but their higher frequency and shorter wavelength allow finer detail to be resolved.
How echo sounding works
When ultrasound meets a boundary between two different media, part of the wave is reflected back.
The time for the reflection to return is measured. Distance = speed × time gives the total path length, which must then be halved because the wave travelled there and back.
Uses
Medical imaging, including pre-natal scanning, because ultrasound does not damage cells as X-rays can.
Industrial imaging to detect cracks and flaws inside objects without cutting them open. Echo sounding to measure the depth of water.
Key points
- Ultrasound is above 20 000 Hz.
- It reflects at boundaries between media.
- Time for the reflection is measured.
- Distance = speed × time, then halve.
- Halving accounts for the there-and-back path.
- Uses include pre-natal scanning and flaw detection.
Worked examples
Example 1
An ultrasound pulse takes 0.006 s to return from a boundary. The speed of sound is 1500 m/s. Calculate the distance to the boundary. [3 marks]
Model answer
Total distance = speed × time = 1500 × 0.006 = 9 m (1 mark). The wave travelled to the boundary and back (1 mark), so the distance to the boundary = 9 ÷ 2 = 4.5 m (1 mark).
Example 2
State two uses of ultrasound. [2 marks]
Model answer
Medical imaging such as pre-natal scanning (1 mark). Industrial imaging to detect flaws or cracks inside objects (1 mark).
Example 3
Explain why the calculated distance must be halved. [2 marks]
Model answer
The ultrasound pulse travels from the source to the boundary and then reflects back to the detector (1 mark), so the total distance calculated is twice the distance to the boundary (1 mark).
Common mistakes
Forgetting to halve the distance.
The wave travels there and back, so the total path is twice the distance.
Saying ultrasound is audible.
It is above the upper limit of human hearing, at more than 20 000 Hz.
Using the wrong speed.
Use the speed of sound in the medium concerned, which differs between air, water and tissue.
Confusing ultrasound with X-rays.
Ultrasound does not ionise, which is why it is safe for pre-natal scanning.
Exam tips
- Always halve the distance for an echo calculation.
- Show the halving as a separate step for the mark.
- Learn two distinct uses.
- Remember this is Triple-only AND Higher-only.
Key terms
- Ultrasound
- Sound with a frequency above 20 000 Hz.
- Echo sounding
- Using reflected pulses to measure distance.
- Boundary
- The interface between two different media.
- Pre-natal scanning
- Medical imaging of a foetus using ultrasound.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.