1) The implied assumption for the initial question about the exponential
cooling was that the "brick" has the same temperature everywhere. The term
"a small metallic sphere" would be more appropriate in my example.
..............................
2) Jim Green asked:
> Could someone please tell me what the "exponential law of cooling"
might be.
and Leigh Palmer answered
> The "law" states that an object approaches the temperature of its
> surroundings at a rate which is exponential in time. If the initial
> temperature of the object is Ti and the temperature of the
> surrounding is To, the temperature varies with time according to
>
> T(t) = To + (Ti-To) exp (-t/tau)
>
> where tau is the time constant for the approach to equilibrium.
The above formula also describes the "law" of exponential decay. Just
replace T(t) by the counting rate due to radioactive atoms, To by the
background rate and tau by the mean life of an atom. IS THIS SIGNIFICANT?
The law of decay can be derived from the assumption that atoms transform
independently of each other and that the probability of decay (per unit
time), 1/tau, is constant.
Ludwik Kowalski