Sonar is used by ships to locate objects on the sea floor. Explain how sonar works, including what type of wave is used and why this wave is suitable for this purpose.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A ship uses sonar equipment to detect a shipwreck resting on the sea floor. The equipment emits a pulse, detects the returning signal, and calculates the depth of the wreck.
Model answer (5 marks)
Sonar uses ultrasound waves.
1. A pulse of ultrasound is emitted from the ship.
2. The pulse travels through water and reflects off the sea floor or an object.
3. The reflected pulse is detected by the ship’s receiver.
4. The time taken for the pulse to return is measured.
5. Ultrasound is suitable because it can travel through water and, as a longitudinal wave, can propagate through fluids.
1. A pulse of ultrasound is emitted from the ship.
2. The pulse travels through water and reflects off the sea floor or an object.
3. The reflected pulse is detected by the ship’s receiver.
4. The time taken for the pulse to return is measured.
5. Ultrasound is suitable because it can travel through water and, as a longitudinal wave, can propagate through fluids.
Examiner tips
- Use the exact phrase "ultrasound waves" and mention they are longitudinal.
- Show the sequence: emission, travel, reflection, detection, time measurement.
- Explain suitability: travel through water and fluid propagation.
- Keep answer concise to fit 5 marks.
Common mistakes
- Confusing sonar with radar or using light waves.
- Omitting the time‑of‑flight measurement.
- Claiming ultrasound is a transverse wave or cannot travel through water.
Mark scheme (5 marks)
- Sonar uses ultrasound waves
- A pulse of ultrasound is emitted from the ship
- The ultrasound reflects off the sea floor / object
- The reflected pulse is detected and the time taken for the pulse to return is measured
- Ultrasound is suitable because it can travel through water / it is a longitudinal wave that can travel through fluids
Key terms in this question
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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