In a wedge-shaped film, between two points X and Y, nine friges are observed with light of wavelength `4800 Å`. How many fringes will be observed between the same two points if the wavelength of light is changed to `6400 Å` ?

Explanation

To solve the problem, we will use the relationship between the number of fringes observed in a wedge-shaped film and the wavelength of light used. The key formula we will use is derived from the interference condition for thin films:

1. **Understanding the relationship**: The number of fringes (n) observed in a wedge-shaped film is given by the formula:
\[ n = \frac{2 \mu \Delta t}{\lambda} \]
where \( \mu \) is the refractive index of the film, \( \Delta t \) is the thickness of the film, and \( \lambda \) is the wavelength of the light.

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