Question

A solid sphere of copper of radius R and a hollow sphere of the same materail of inner radius r and outer radius A are heated to the same temperature and allowed to cool in the same environment. Which of tehm starts cooling faster?

Answer 1

Since the temperature and surface area is same,
therefore the energy emitted per second by both spheres is
same.
We know that `Q=mcDeltaT`
Since Q is same and c is also same (both copper).
`:. Mprop1/(DeltaT)`
Mass of hollow sphere is less,
`:.` Temperature change will be more.
`:.` Hollow sphere will cool faster.