Soap bubbles

Immerse the ring in the cup of shampoo and then blow steadily but slow through it. Everyone of us must have made such bubbles when we were young. But have you watched carefully how they shimmer with all the colours of rainbow?

This is called light interference on thin films. If a one-coloured light beam falls on the surface of the film, it partly reflects and partly filter through the film undergoing refraction. Some of the beams that managed to filter through escape through the other side of the bubble. Some of those get reflected and are refracted on the opposite surface. Which colour is created and which not depends on the thickness of the film.

These phenomena have always fascinated people not only with their beauty, but also with the fact that they can be observed in short-lasting objects like bubbles, oil spills on water, oil slicks on a wet road, insects' wings, mother-of-pearl and peacock's tail.