1) Assuming the light hits perpendicular to the wall of the soap bubble, what is

Question

1) Assuming the light hits perpendicular to the wall of the soap bubble, what is the minimum thickness it could have to produce completely constructive interference for violet light (? = 400 nm)? tconstr = ___ nm

2) What is the minimum thickness it could have to produce completely destructive interference for this same violet light? tdestr= ___ nm

3) What is the minimum thickness it could have to produce completely destructive interference for violet light (? = 400 nm)? tdestr= ___ nm

Explanation / Answer

1) Phase diff. due to 1st-surface reflection = .5 cycles (N1<N2)
Phase diff. due to 2nd-surface reflection = 0 cycles (N2>N3)
Phase diff. due to both reflections = .5 cycles.
phase diff. due to pathlength d = integer(incl. 0) + 0.5 cycles.
Wavelength in film lambda2 = lambda1/N2 = 305.34nm
Tmin = lambda2*(1-d)/2 = lambda2/4 = 76.34 nm

2) phase diff. due to pathlength d = integer no. of cycles.
Wavelength in film lambda2 = lambda1/N2 = 497.709923664122 nm
Tmin = lambda2*(1-d)/2 = lambda2/2 = 157.7 nm

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