An ideal black body at room temperature is thrown into a furnace. It is observed that:

In which of the following phenomena do heat waves travel along straight lines with the speed of light?

Why are the bottom layers of cooking vessels kept black in color?

$A$ certain substance emits only the wavelengths ${\lambda _1}, {\lambda _2}, {\lambda _3}$ and ${\lambda _4}$ when it is at a high temperature. When this substance is at a colder temperature,it will absorb only the following wavelengths:

''$A$ perfect black body is black in colour.'' Is this statement true or false?

$A$ solid cylinder of length $L$ and radius $r$ is heated up to the same temperature as that of a cube of edge length $a$. If both have the same material,volume,and are allowed to cool under similar conditions,then the ratio of the amount of radiation emitted will be (Neglect radiation emitted from the flat surfaces of the cylinder).