The white strip of paper can be bent around the bubble to better see the fringes. Keep making bubbles. Watch the color patterns on the bubble. The colors will slowly go around the bubble and form rings, then a black dot will form in the middle of the bubble and it will pop. As students experiment, share that the colors we see on the bubble are the reflection of white light shining on the bubble film.
White light has many colors - each color has a different wavelength.
When the crests of one wave meets the trough of another wave, the waves cancel each other out and we see destructive interference. As a bubble film thins out, the colors cancel each other out until all we see is a black dot in the middle of the bubble. Discussion Review with students what intereference is. We get interference from a thin film like a bubble, because the light waves which bounce off the front and back surfaces of the bubble wall add constructively or destructively. Whether you get destructive or constructive interference depends on the color of the light and the thickness of the bubble.