Sound wavesIB MYP Sciences: Subtopic test

1. 1
   Astronauts on a spacewalk outside a space station cannot hear each other speak, even when they are only one metre apart, so they talk by radio. Inside the station, where there is air, the same astronauts can talk normally.

   (a)

   Why can the astronauts not hear each other directly when they are outside the station?

   [1 mark]

   • ASound travels too slowly to cross a distance of one metre
   • BSound needs particles to vibrate and pass the energy on, and space is almost a vacuum
   • CSound waves are absorbed by the astronauts' spacesuits
   • DSpace is too cold for sound to travel

   (b)

   What type of wave is the sound the astronauts hear inside the station?

   [1 mark]

   • ATransverse, because the air particles move at right angles to the direction of travel
   • BElectromagnetic, because it can carry a message
   • CLongitudinal, because the air particles vibrate parallel to the direction of travel
   • DTransverse, because it has compressions and rarefactions

   (c)

   Describe what is meant by a compression and by a rarefaction in a sound wave.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hiker in a valley in Switzerland shouts towards a large cliff and hears her echo 0.80 s later. The speed of sound in air is 340 m/s.

   (a)

   Why does the hiker hear an echo?

   [1 mark]

   • AThe sound is absorbed by the cliff and re-emitted later
   • BThe sound is diffracted around the cliff
   • CThe sound speeds up when it reaches the cliff
   • DThe sound is reflected by the cliff and travels back to her

   (b)

   What is the total distance travelled by the sound between her shout and the echo reaching her?

   [1 mark]

   • A272 m
   • B136 m
   • C425 m
   • D0.0024 m

   (c)

   The hiker walks to a new position, shouts again and hears the echo 1.2 s later. Calculate her new distance from the cliff.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students in Cairo measure the speed of sound in air. They stand 100 m from a large flat wall and clap their hands. A partner uses a stopwatch to time the delay between the clap and the echo. Five repeat readings are 0.66 s, 0.54 s, 0.62 s, 0.55 s and 0.58 s. The students know that the accepted speed of sound in air is about 340 m/s.

   (a)

   Calculate the mean time and use it to find the speed of sound in air from the students' results.

   [3 marks]

   (b)

   Evaluate the students' method and suggest two improvements.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Hospitals use ultrasound scanners to look at unborn babies. The scanner sends pulses of sound with a frequency of 3.0 MHz into the body and detects the echoes from boundaries between tissues. Ultrasound travels at about 1500 m/s in soft tissue. Ultrasound scanners are cheaper and safer than many other scanners, but trained operators are scarce in some rural areas, and in some places scans have been misused to find out the sex of a baby so that parents can act on it.

   (a)

   (i) Explain why the mother cannot hear the ultrasound pulses. (ii) The echo from the baby's skull returns to the scanner 0.000 080 s after the pulse is sent. Calculate the depth of the skull below the scanner.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of using ultrasound scans on pregnant women, and evaluate whether every pregnancy should be offered a scan.

   [6 marks]

   Total for question 4: 12 marks

End of questions