1. 1
   A guitarist plucks a string on an acoustic guitar, and the vibrating string causes the surrounding air to compress and stretch in a regular pattern, producing a sound that travels to a listener's ears.

   (a)

   What type of wave is a sound wave travelling through air?

   [1 mark]

   • AA longitudinal wave
   • BA transverse wave
   • CAn electromagnetic wave
   • DA standing water wave

   (b)

   What is required for the sound produced by the guitar string to travel through the air to the listener's ears?

   [1 mark]

   • AA source of visible light travelling alongside the sound wave
   • BNothing at all, sound can travel just as well through a complete vacuum
   • CDirect physical contact between the listener's ear and the guitar string
   • DA medium, such as the air, through which the vibrations can be transmitted

   (c)

   Describe, in terms of compressions and rarefactions, how the vibrating guitar string produces a sound wave that travels through the surrounding air.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A dog trainer uses a special whistle that produces a sound at a frequency of 25000 Hz to give commands to a dog. The trainer cannot hear the whistle at all, but the dog responds to it immediately.

   (a)

   Why can the trainer not hear the sound from the whistle?

   [1 mark]

   • ASound waves at this frequency travel too slowly to reach the trainer's ears
   • BThe whistle does not actually produce any sound waves at all
   • CThe frequency of 25000 Hz is above the upper limit of the typical range of human hearing, which is approximately 20 Hz to 20000 Hz
   • DThe whistle only produces electromagnetic waves, not sound waves

   (b)

   What term is used to describe sound with a frequency higher than 20 kHz, such as that produced by this dog whistle?

   [1 mark]

   • AInfrasound
   • BUltrasound
   • CUltraviolet sound
   • DRadiofrequency sound

   (c)

   State the approximate range of frequencies that are typically audible to humans, and explain why the dog, unlike the trainer, is able to hear the 25000 Hz whistle.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of students stands at one end of a long, straight canyon and shouts loudly, then times how long it takes to hear a clear echo returning from a distant canyon wall.

   (a)

   (a) Describe how the students could use their observations of the shout and the returning echo, along with the known speed of sound in air, to calculate the distance to the canyon wall.

   [3 marks]

   (b)

   The students measure a time of 2.4 seconds between the shout and hearing the echo, and use a value of 340 m/s for the speed of sound in air. Calculate the distance to the canyon wall, showing your working, and explain why an echo could not be heard in a similar way if the canyon walls were replaced with a very soft, thick layer of loose sand or foam instead of hard rock.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital uses an ultrasound scanner to examine a pregnant patient's unborn baby, sending pulses of high-frequency ultrasound into the patient's abdomen and detecting the reflected pulses that bounce back from different boundaries between different types of soft tissue inside the body, such as the boundary between amniotic fluid and the baby's skin.

   (a)

   Explain fully how the ultrasound scanner uses the reflected pulses and the known speed of sound in soft tissue to build up an image of the structures inside the body, and explain why ultrasound is generally considered a safer imaging method for use during pregnancy than an alternative technique such as X-ray imaging.

   [6 marks]

   (b)

   An engineering firm adapts the same underlying ultrasound reflection principle used in medical scanning to design a sonar system for a ship, which sends pulses of ultrasound down into the sea and times how long it takes for the reflected pulse to return from the seabed. Explain fully how this sonar system calculates the depth of the seabed beneath the ship, and explain what would happen to the calculated depth reading if the ship's crew mistakenly used the speed of sound in air, rather than the correct, much greater speed of sound in seawater, in their calculation.

   [6 marks]

   Total for question 4: 12 marks

End of questions