The colors you see in soap films are due to the interference effect. Assume that
ID: 1418452 • Letter: T
Question
The colors you see in soap films are due to the interference effect. Assume that the interference effect is mainly due to the water molecules (index 1.33). Consider a 450nm thick soap film. Upon reflection, what wavelength(s) of visible light will destructively interfere? Upon reflection, what wavelength(s) of visible light will constructively interfere? As the water evaporates, the film will decrease in thickness. After a few minutes the thickness has dropped to l00nm. How do your answers change for a) and b)?Explanation / Answer
2nt = ( m+1/2) lamda
lamda = t 4n/ ( 2 m+1)
= 450 nm ( 4( 1.33)/ 2( 0) + 1)
=2394 nm
lamda = t 4n/ ( 2 m+1)
= 450 nm ( 4( 1.33)/ 2( 1) + 1)
=798nm
lamda = t 4n/ ( 2 m+1)
= 450 nm ( 4( 1.33)/ 2( 2) + 1)
=478.8nm
lamda = t 4n/ ( 2 m+1)
= 450 nm ( 4( 1.33)/ 2( 3) + 1)
=342nm
construtive interference occurs 478.8 nm
distructive intereference condition is
2nt = m lamda
lamda = 2nt/ m
m = 1
lamda = 2(1.33) ( 450 nm)
=1197 nm
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(c)
lamda = t 4n/ ( 2 m+1)
= 100 nm ( 4( 1.33)/ 2( 0) + 1)
=532 nm
lamda = t 4n/ ( 2 m+1)
= 100 nm ( 4( 1.33)/ 2( 1) + 1)
=177.33
construtive interference occurs 177.33 nm
lamda = 2nt/ m
m = 1
lamda = 2(1.33) ( 100 nm)
=266 nm
m= 2(1.33) ( 100 nm) /2
=133 nm
m= 2(1.33) ( 100 nm) /3
=88.66 nm
m= 2(1.33) ( 100 nm) /4
=66.5 nm
distrucitive interference occurs 133 nm,88.66 nm,66.5 nm, ........