Page 51 - Basic Electrical Engineering

−3
α = 3.7 × 10 /°C
20

We can write,

R = R [1+ α (t − t )]
3
1
1 3
1
substituting,
−3
21 = 18 [1 + 3.7 × 10 (t −20)]
3
or,

t = 65°C.
3

Example 1.9 The resistance of a wire increases from 40 Ω at 20°C to 50 Ω
at 70°C. Calculate the temp. coefficient of resistance at 0°C.

Solution:

given
R = 40 Ω, R =50 Ω, what is α ?
70
20
°
R = R [1 + α (t − t )]
1 2
1
2
1
50 = 40[1+α (70 −20)]
1
−3
α = 5 ×10 /°C
1

or,

or,

−3
α = 5.55 × 10 /°C
0