In which mode of transmission, the heat waves travel along straight line with the speed of light?

Consider a compound slab consisting of two different materials having equal lengths, thickness and thermal conductivities K and 2K respectively. The equivalent thermal conductivity of the slab is

In an adiabatic process with the ratio of two specific heat, $$\gamma=\frac{3}{2}$$, pressure is increased by $$\frac{2}{3}$$%, then decrease in the volume will be

For an ideal gas, coefficient of volume expansion is given by