A solid rectangular sheet has two different coefficients of linear expansion $$\alpha$$₁ and $$\alpha$$₂ along its length and breadth respectively. The coefficient of surface expansion is (for $$\alpha$$₁ t << 1, $$\alpha$$₂t < <1)

A gas bubble of 2 cm diameter rises through a liquid of density 1.75 g cm^$$-$$3 with a fixed speed of 0.35 cms^$$-$$1. Neglect the density of the gas. The coefficient of viscosity of the liquid is

1000 droplets of water having 2 mm diameter each coalesce to form a single drop. Given the surface tension of water is 0.072 Nm^$$-$$1. The energy loss in the process is