Could someone please help me? I just can\'t get the hang ofthis stuff! A loop of

Question

Could someone please help me? I just can't get the hang ofthis stuff! A loop of wire is dipped in soapy water and held so that thesoap film is vertical. The top of the film appears black. Why?Below the black region there are colored bands. Is the first bandred or violet? Could someone please help me? I just can't get the hang ofthis stuff! A loop of wire is dipped in soapy water and held so that thesoap film is vertical. The top of the film appears black. Why?Below the black region there are colored bands. Is the first bandred or violet?

Explanation / Answer

refractive index of the soap water = n, thickness of the film =t path difference = 2nt + /2 at the top, t --> 0, = /2, so the destructiveinterference happens there for any wavelength, so black there. from top to bottom, t is increasing, when = 2nt + /2 =, or = 4nt, constructive interference happens andappears bright, the shortest wavelength appears bright first, orviolet is the first band.

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