A thin film of soap solution () lies on the top of a glass plate (). When visible light is incident almost normal to the plate, two adjacent reflection maxima are observed at two wavelengths and . The minimum thickness of the soap solution is
Step 1: Given Data:
Refractive index of soap solution,
Refractive index of glass,
Two adjacent reflection maxima are observed at two wavelengths,
Let the thickness of the soap solution is .
Step 2: We have to find the minimum thickness of the soap solution is,
For reflection at the air-soap solution interface, the phase difference is.
For reflection at the interface of soap solution to glass also, there will be a phase difference of .
The condition for maximum intensity:
(where, is the refractive index and is order)
Step 3: For order :
As we know, the formula of refractive index is
Step 4: Maximum order, where they coincide:
Hence, the correct option is (C).