• Question: Why does light and sound travel in different types of waves and not the same?

    Asked by Meg to Chris, Josh, Rebecca, Susan on 24 Jun 2015. This question was also asked by Mia.
    • Photo: Rebecca Dewey

      Rebecca Dewey answered on 24 Jun 2015:


      Light is both a wave and a particle – it is carried by the particle we call the photon. Photons are an actual measurable thing and can continue to exist and to travel, even in a vacuum (where there is no air or any other matter).

      Sound is a wave or vibration that is being passed through another form of matter, such as air, or water, or metal. If it weren’t for the air/water/metal, then the sound waves wouldn’t exist because there is no matter there to vibrate.

    • Photo: Susan Cartwright

      Susan Cartwright answered on 24 Jun 2015:


      Light and sound are *completely* different, unrelated things. The only thing they have in common is that they are both waves!

      Sound is a travelling pressure wave, consisting of alternating regions of high and low density. Individual particles oscillate back and forth along the direction of the sound wave (it’s a longitudinal wave). Sound waves need to travel through something – sound cannot travel in a vacuum, and the denser the material, usually the faster the sound travels.

      Light cannot possibly be a longitudinal wave, because that would require bits of it to be moving faster than, er, light! It’s a transverse wave produced by crossed electric and magnetic fields (that’s why light is sometimes called electromagnetic radiation). Light is perfectly happy travelling in a vacuum; if it travels through something, then typically the denser the “something”, the slower the light travels.

      Since they have nothing in common, there’s no reason to expect that they would look the same – and they don’t.

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