P. 4172. With appropriate washing-up liquids the surface tension of water can be significantly decreased. If a frame is immersed into a mixture of water and washing-up liquid, and then it is carefully taken out, there will be a thin layer of soap film on the frame. Coloured stripes can be observed on the soap film (if it is in front of a black background.)
a) What is the direction of the stripes if the plane of the frame is vertical? Why do they have this direction?
b) What is the colour of the film if its width is only 10-8 m?
Deadline expired on 11 June 2009.