Sound Waves
3 marks · NormalSound waves can be reflected and refracted much like light.
Describe what happens when a sound wave meets a flat, hard surface such as a wall.
Explain how ships use echoes to measure the depth of the sea below them.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) It is reflected; the sound wave bounces off the surface as an echo.
(b) Ships emit a sound pulse which travels to the seabed. The sound reflects back as an echo and is detected. The time taken for the echo's return is measured, and the depth is calculated using speed = distance/time.
Common mistakes: Not mentioning time for sound's return, or double travel
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States the sound is reflected / produces an echo.
B1 (b) · 1 mark · Describes sending a sound wave (pulse) down, echo returns from seabed.
B1 (b) · 1 mark · Mentions measurement of time and calculation of depth using speed of sound.
Worked solution
a) The sound wave is reflected off the wall, producing an echo.
b) The ship emits a sound pulse downwards. The sound travels to the seabed and is reflected back as an echo. The time for the echo to return is measured, and the depth is calculated using the speed of sound and the time (knowing the sound travels down and back).