A uniform brass disc of radius and mass m is set into spinning with angular speed ${\mathrm{\omega }}_0$, about are axis passing through centre of disc and perpendicular to the plane of disc. If its temperature increases from ${{\mathrm{\theta }}_1}^{\circ }\mathrm{C}\text{ to }{{\mathrm{\theta }}_2}^{\circ }\mathrm{C}$ without disturbing the disc, what will be its new angular speed ? (the coefficient of linear expansion of brass is $\mathrm{\alpha }$)