# Interaction between blackbodies in relation to the second law

1. Oct 24, 2011

### Shunyata

I am trying to understand the behavior of blackbodies in interaction with each other.

Conditions as follows.

$1)$ There are two blackbodies, say $B_1$ and $B_2$, with corresponding temperature $T_1$ and $T_2$.

$2)$ Initially $T_1>T_2$.

$3)$ $B_1$ and $B_2$ have thermal contact only through radiation exchange.

And finally my question,

Can $B_2$ give energy to $B_1$ or is this prevented by the second law?

2. Oct 24, 2011

### cjl

Sure it can. In fact, it always will be. However, B1 will always be giving more energy to B2 than the reciprocal effect, so the net energy exchange will always involve B1 giving energy to B2.

3. Oct 24, 2011

### Shunyata

Is it as simple as

$dQ\Big( \frac{1}{T_2} - \frac{1}{T_1}\Big)=dQ\Big( \frac{T_1-T_2}{T_1T_2}\Big)>0,$

if $dQ=dQ_1 - dQ_2$ is the net-heat where positive direction is from $B_1$ to $B_2$ and $dQ_1>dQ_2$?