57. From Eq. 41-29, N
2
/N
1
= e
−(E
−E
)/kT
. We solve for T :
T =
E
− E
k ln(N
)
=
3.2 eV
(1.38
× 10
−23
J/K ) ln(2.5
15
/6.1
13
= 10000 K .