A Young’s double slit interference arrangement with slits $$S_1$$ and $$S_2$$ is immersed in water (refractive index = $$\frac{4}{3}$$) as shown in the figure. The positions of maxima on the surface of water are given by $$x^2 = p^2m^2 \lambda^2 - d^2$$, where $$\lambda$$ is the wave length of light in air (refractive index = 1), 2d is the separation between theslits and m is an integer. The valueofp is