# A student places a ringing mobile phone inside a sealed glass jar. As the air is slowly pumped out of the jar, the sound of the ringing becomes quieter and eventually cannot be heard at all, even though the phone can still be seen vibrating. Explain these observations.

> Eduqas GCSE Physics — 5.1 Waves in air, fluids and solids · Explain · 4 marks

## Mark scheme (4 marks)

1. Sound requires a medium (material/particles) to travel through
2. As air is removed, fewer particles are present to transmit the sound wave / vibrations
3. When all (most) air is removed a vacuum is formed, so no particles remain to transmit the sound, and no sound is heard
4. Light (unlike sound) does not need a medium / can travel through a vacuum, which is why the phone can still be seen

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-places-a-ringing-mobile-d2f2c432) · Published by Druglandscape Ltd.