1. 1
   A technician taps a tuning fork and holds it close to a microphone connected to an oscilloscope. The oscilloscope trace shows a repeating wave pattern. The technician wants to identify the type of wave a sound wave is, and how the vibrations of the tuning fork's prongs create this wave in the surrounding air.

   (a)

   Which type of wave is a sound wave?

   [1 mark]

   • AA longitudinal wave
   • BA transverse wave
   • CAn electromagnetic wave
   • DA standing wave that does not transfer energy

   (b)

   The tuning fork vibrates and pushes air molecules together and apart as it moves. What name is given to the regions where the air molecules are pushed closer together?

   [1 mark]

   • ARarefactions
   • BCompressions
   • CWavefronts
   • DNodes

   (c)

   The technician then repeats the experiment inside a bell jar, from which the air is slowly pumped out using a vacuum pump. Describe what happens to the loudness of the sound heard as the air is removed, and explain why this happens in terms of what a sound wave needs in order to travel.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A veterinary clinic uses an ultrasound scanner to examine the internal organs of a large dog. The scanner emits sound waves at a frequency far higher than a human can hear and detects the reflections that return from the boundaries between different tissues inside the dog's body.

   (a)

   What is the approximate minimum frequency of the sound waves used for ultrasound scanning?

   [1 mark]

   • A20 Hz
   • B200 Hz
   • C2000 Hz
   • D20000 Hz

   (b)

   As the ultrasound waves travel from the dog's soft tissue into a denser layer of tissue, their speed changes. This change in speed at the boundary between the two tissues, together with a change in direction, is an example of which process?

   [1 mark]

   • AReflection
   • BDiffraction
   • CRefraction
   • DPolarisation

   (c)

   Some of the ultrasound wave energy is reflected at each tissue boundary and returns to a detector in the scanner, while some continues onward through the tissue. The scanner measures the time delay between sending a pulse and receiving its reflection to work out the depth of a boundary inside the dog. Explain, in terms of wave speed and time, how the scanner uses this time delay to calculate the depth of a tissue boundary.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A geologist is investigating the structure of the Earth's core by studying seismic waves generated by an earthquake, which behave in a similar way to sound waves travelling through different materials. Seismic detector stations around the world record that certain types of seismic wave fail to reach detectors on the far side of the Earth, appearing instead in a 'shadow zone', while others pass through more directly.

   (a)

   Explain, using ideas about how waves such as sound waves interact with material boundaries, why the properties of the waves reaching different detector stations change as the waves pass through the different layers of the Earth.

   [3 marks]

   (b)

   A particular seismic wave pulse is measured leaving the earthquake source and arriving at a detector station a distance of 6000 km away, taking 1000 seconds to arrive, having travelled through a layer of roughly constant density for the whole journey. Calculate the average speed of this seismic wave, giving your answer in km/s.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital is choosing between two medical imaging techniques for examining a patient's soft tissue: an ultrasound scan (using high-frequency sound waves reflected from internal tissue boundaries) and an X-ray scan (using electromagnetic radiation absorbed by different tissues to different extents). The hospital is also considering how ultrasound could help a search-and-rescue team locate survivors in a partially collapsed building.

   (a)

   Evaluate the use of ultrasound compared with X-rays for imaging soft tissue in this situation, referring to how each type of wave interacts with the body and the risks and benefits of each method.

   [6 marks]

   (b)

   The hospital is also considering how ultrasound could be used to help a search-and-rescue team locate survivors in a partially collapsed building, in a way similar to how it is used medically to detect internal boundaries. Construct an explanation of how a device could use reflected sound/ultrasound waves and knowledge of wave speed to detect and estimate the distance to solid objects or voids hidden within the rubble, and discuss one limitation of this approach.

   [6 marks]

   Total for question 4: 12 marks

End of questions