AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Echo sounding, using high frequency sound waves is used to detect objects…
Full specification wording
Waves for detection and exploration (physics only) (HT only): Echo sounding, using high frequency sound waves is used to detect objects in deep water and measure water depth.
Echo sounding is the same timing method as an ultrasound scan, carried out in water.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 11 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Echo sounding is the same timing method as an ultrasound scan, carried out in water. A ship sends a short pulse of high frequency sound downwards, the pulse reflects from the sea bed, a shoal of fish or a wreck, and a detector on the hull records the time for the echo to return. Because the pulse travels down and back, the depth is (v × t) / 2 with v the speed of sound in sea water, about 1500 m/s. A pulse returning after 0.4 s therefore comes from a depth of 1500 × 0.4 / 2 = 300 m. High frequencies are used because the shorter wavelength reflects well from small objects and gives better resolution. Repeating the measurement along the ship track builds a profile of the sea bed.
What earns the marks
- Stating that a pulse of sound is sent out and the time for its echo to return is measured.
- Using speed = distance / time with the speed of sound in water.
- Halving the distance because the pulse travels down and back.
- The depth given with a correct unit.
Common mistakes and how to put them right
Using the speed of sound in air, about 330 m/s, for a pulse travelling in water.
Omitting the halving step and reporting double the true depth.
Saying high frequency is used because it is louder rather than for the shorter wavelength and finer detail.
Giving the answer in seconds rather than metres after a distance calculation.
Exam tips
- Set the calculation out in three lines: total distance, then halve it, then state the unit.
- Read the stem for the speed of sound in water; it is normally supplied and may not be 1500 m/s.
- If the question mentions detecting fish or a wreck, mention resolution when you justify high frequency.
Try the lesson
The start of the Waves for detection and exploration (physics only) (HT only): Echo sounding, using high frequency sound waves is used to detect objects in deep water and measure water depth. lesson, made from checked teaching notes for this specification point.
Have a go first
A ship uses echo sounding to measure the depth of water beneath it. A high frequency sound wave is sent downwards and its reflection is detected 0.80 s later. The speed of sound in water is 1500 m/s. What is the depth of the water?
Listen
Echo sounding is the same timing method as an ultrasound scan, carried out in water. A ship sends a short pulse of high frequency sound downwards, the pulse reflects from the sea bed, a shoal of fish or a wreck, and a detector on the hull records the time for the echo to return. Because the pulse travels down and back, the depth is (v × t) / 2 with v the speed of sound in sea water, about 1500 m/s. A pulse returning after 0.4 s therefore comes from a depth of 1500 × 0.4 / 2 = 300 m. High frequencies are used because the shorter wavelength reflects well from small objects and gives better resolution. Repeating the measurement along the ship track builds a profile of the sea bed. A strong answer earns marks for these points. stating that a pulse of sound is sent out and the time for its echo to return is measured. using speed = distance / time with the speed of sound in water. halving the distance because the pulse travels down and back. the depth given with a correct unit. Exam tip: Set the calculation out in three lines: total distance, then halve it, then state the unit.
Key words
Say what each word means before you turn the card.
echo sounding
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halving the path
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speed of sound in water
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resolution
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See every definition
- echo sounding
- Using high frequency sound waves to detect objects in deep water and measure water depth.
- halving the path
- Dividing the total distance by two because the pulse travels down and back.
- speed of sound in water
- The speed used with speed = distance / time for a pulse travelling in water, about 1500 m/s in sea water.
- resolution
- The finer detail given by the shorter wavelength of high frequencies, which reflects well from small objects.
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