25. The resistance at operating temperature T is R = V /i = 2.9 V/0.30 A = 9.67 Ω. Thus, from R
− R
0
=
R
0
α(T
− T
0
), we find
T
=
T
0
+
1
α
R
R
0
− 1
=
20
◦
C +
1
4.5
× 10
−3
/K
9.67 Ω
1.1 Ω
− 1
which yields approximately 1900
◦
C. Since a change in Celsius is equivalent to a change on the Kelvin
temperature scale, the value of α used in this calculation is not inconsistent with the other units involved.
Table 27-1 has been used.