Sonar is used by ships to detect objects beneath the surface of the water. Describe how sonar works and explain why ultrasound waves, rather than sound waves within the human hearing range, are used for this purpose.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A ship uses sonar equipment to map the seabed and detect shoals of fish beneath it.
Model answer (5 marks)
Ultrasound waves are emitted from the ship into the water.
The waves travel until they encounter an object such as the seabed or a shoal of fish, where they are reflected back to the ship.
The ship measures the time taken for the reflected waves to return and uses this to calculate the distance to the object.
Ultrasound waves have a frequency higher than the upper limit of human hearing (above 20 kHz).
Because the wavelength is shorter, ultrasound can detect smaller objects and produce a more detailed, precise image.
The waves travel until they encounter an object such as the seabed or a shoal of fish, where they are reflected back to the ship.
The ship measures the time taken for the reflected waves to return and uses this to calculate the distance to the object.
Ultrasound waves have a frequency higher than the upper limit of human hearing (above 20 kHz).
Because the wavelength is shorter, ultrasound can detect smaller objects and produce a more detailed, precise image.
Examiner tips
- Use the word "ultrasound" and specify the frequency range (>20 kHz).
- Explain the time‑of‑flight calculation for distance.
- Mention the shorter wavelength gives higher resolution.
Common mistakes
- Confusing audible sound with ultrasound; forgetting the frequency detail.
- Omitting the time‑of‑flight distance calculation.
Mark scheme (5 marks)
- Ultrasound waves are emitted from the ship (into the water)
- The ultrasound waves reflect off the object / seabed / fish and return to the ship
- The time taken for the waves to return is measured / used to calculate distance
- Ultrasound waves have a frequency higher than the upper limit of human hearing (above 20 kHz)
- Ultrasound has a shorter wavelength so can detect smaller objects / gives a more detailed / precise image
Key terms in this question
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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