A monochromatic light of wavelength '$\lambda$' is incident on two slits $S_1$ and $S_2$ made on x-axis. The midpoint of the line $S_1{S}_2$ is considered as origin and ‘$d$’ is the distance between the two slits which are symmetric about y-axis. The interference pattern is observed on a plate of mass M which is acting as a screen. The screen is attached to one end of a vertical spring of spring constant ‘$k$’ and the other end of spring is attached with the ground. Spring is massless and screen always remains in horizontal plane. The distance between the plane of slits and the screen is $D (D>>d)$. Assuming $S_1$ and $S_2$ are coherent in nature. At t = 0, screen is released and spring is in its natural length. It is given that $M$ = 1kg, $k$ = 1 N/m. $D=\frac{5Mg}{k},g=10m/s^2,d=200\lambda$ .The x co-ordinate (in cm) of the first order maxima on the screen as a function of time is given by $\pm ({\lambda }_1-{\lambda }_2\cos t) cm.$