[thedoc (OP)]

Kevin Fitch  asked the Naked Scientists:
   Why are small bubbles white but large bubbles are see through?

Love the show!

Kevin and William Fitch
Glenwood, Maryland, USA


What do you think?

[Kryptid]

Here's my best guess.

I think that small bubbles are indeed transparent as well. Bubbles reflect, distort and trasmit light. However, the amount and degree is probably dependent in part on the size and number of bubbles present. If you have a single, fist-sized bubble, you can see shiny spots on it from the light it reflects but you can also see through it. A collection of small bubbles (such as in the foam generated in a bubble bath) will have a very large number of bubbles per unit volume (each one of which reflects and distorts light). This massive collection of reflections and distortions makes it harder to see through the mass as light has more trouble travelling in a straight line through it. A similar phenomenon is likely responsible for why snow is white even though it is made of ice. Each individual ice particle in the snow distorts light and breaks up any image of what lies under it.

[dlorde]

It probably depends what sort of bubbles you're talking about. Air bubbles under water look and behave differently to soap bubbles in air. But the curvature and surface to volume ratio of bubbles varies with size. I'm guessing the high curvature of small bubbles will scatter most of the incident light by reflection and refraction, making a mass of small bubbles diffuse the light and appear opaque, whereas larger bubbles with their greater volume and lower surface curvature allow correspondingly more light through and reflect & refract a lower proportion of it.

Which seems to be pretty much what Supercryptid said