Q1.
If there is no medium (i.e., no particles), is the propagation of sound waves possible?
Answer
No. Without a material medium, sound waves cannot propagate.
A sound wave is a pattern of higher and lower particle density. If there are no particles, there is no density to raise or lower, and nothing to collide and hand the disturbance forward. Waves that need a material medium in this way are called mechanical waves, and sound is one of them.
| Mechanical wave | Non-mechanical wave | |
|---|---|---|
| Needs a medium? | Yes | No |
| Examples | Sound; waves on a slinky; seismic waves | Light |
| Can cross vacuum? | No | Yes — which is why sunlight and starlight reach the Earth |
| Type | Sound is longitudinal; seismic waves can be either | Light is transverse |
Did you know? Earthquakes send out both kinds of mechanical wave through the Earth. The longitudinal seismic waves travel fastest and are the first to be picked up by a seismograph, which is why they are used to give the earliest earthquake warnings.