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Soap bubbles appear coloured when seen in white light. This is mainly due to:

1. interference
2. scattering
3. diffraction
4. dispersion

Correct answer: interference

Solution

Light reflecting off the top and bottom surfaces of the thin soap film recombines. Depending on the film thickness and the wavelength, certain colours interfere constructively and others destructively, producing the observed colours. This is thin-film interference.

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