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GCSE Questions - Waves

Q9. Ultrasound can be used to produce an image of an unborn baby.

(a)

(i) What is ultrasound?

Sound with a higher frequency than humans can hear (20,000 Hz)

[1 mark]

(ii) What happens to the ultrasound when it reaches the skin of an unborn baby? Tick one of the following:

It is all reflected and none is transmitted.  
Some is reflected and some is transmitted.
None is reflected and it is all transmitted.  

[1 mark]

(iii) Tick a medical use of ultrasound.

breaking up kidney stones
treating cancer  
destroying bacteria  

[1 mark]

(b) A parking sensor on the back of a car emits an ultrasound pulse and receives the reflected pulse as shown in the graphic below.

Complete the sentence to describe how the time taken for the reflected pulse to return to the car changes as the car moves.

As the car moves closer to the wall the reflected pulse takes less (a shorter) time to return to the car.

[1 mark]

(c) The parking sensor emits an ultrasound pulse. The reflected pulse is received 0.006 seconds later. The speed of ultrasound in air is 330 m/s. Calculate the distance from the car to the wall.

Let d be the distance from the wall

In between emitting and receieving the reflection the sound travels a distance 2d

Speed = distance travelled/ time taken

330 = 2d/0.006

d = 330 x 0.006/2

d = 0.99 m

[3 marks]

(d) There are four parking sensors spaced equally along the back of the car. Suggest one advantage of using four sensors instead of just using one sensor.

Any one from:

It is more reliable - if one breaks the others will still work

They can detect smaller objects

They can detect objects over a wider range - it is more accurate

They can detect the position of objects

[1 mark]

(Total 8 marks)