Question

Soap bubble fluid has an index of refraction about the same as water $(n=1.33)$. If the thickness of a particular soap bubble is $122nm$ thick at a certain spot, what wavelength of light is being most strongly reflected from the spot on the bubble?

• A. $325nm$
• B. $216nm$
• C. $467nm$
• D. $649nm$
• E. $587nm$

Answer 1

The correct option is D $649nm$

Given - $n=1.33,t=122nm$,

we have, condition for strong reflection ,

$2nt=(2m+1)\lambda /2$ ,

or $\lambda =4nt/(2m+1)$

for being most strongly reflected, (for $\lambda =maximum$, m=0) ,

therefore ${\lambda }_{max}=4nt$ ,

or ${\lambda }_{max}=4\times 1.33\times 122=649nm$,

this wavelength lie in visible region, so this will be reflected most strongly .