Answer
The pattern will become narrower.
Work Step by Step
Equation 35.6 gives the position of the mth bright band in a 2-slip interference pattern.
$$y_m=R\frac{m \lambda}{d}$$
When the apparatus is immersed in water, the wavelength of the light decreases by a factor of 1.33, water’s index of refraction. All of the fringes move toward the centerline of the pattern, making the pattern more narrow by a factor of 1.33.
