Elements of Electrical Engineering Temperature Co-efficient for Resistance

1. G. H. Patel College of Engineering
and Technology
Subject : Elements of Electrical Engineering
Subject Code : 2110005
Topic : Temperature Co-efficient for Resistance
Made by :
Vashi Bhavik EN:160110116061
Parmar Kelvin EN:160110116027

2. Temperature Co-efficient for
Resistance
•Resistance of almost material is changes with change in
temperature.
•Suppose R0= Resistance of material at 0oC temperature
Rt =Resistance of material at toC temperature
So change in resistance = Rt - R0
R= Rt - R0

3. •Change in resistance is found that
(I) Directly proportional to change in
temperature
(II) Directly proportional to its original , initial
resistance
So from (I) R t
R (t-o)
R t
(II) R R0
R R0 t

4. R R0 t
R= R0 t
• = Temperature co-efficient for
resistance
•“Temperature co-efficient for resistance is
termed as change in resistance per unit rise
in temperature per ohm original(initial)
resistance.”
•Normally is taken at 0oC so

5. = R / ( R0 t )
= (Rt - R0) / ( R0 t )
Rt = R0 [ 1 + 0 t ]
At any temperature resistance of material is
governered by above property.

6. • If we plot graph of R t for copper we got strait
line , slope of R t graph is constant ; if we
extend graph backward it intersection with
horizontal at (-234.5oC).

7. •Slope of graph = R / t
•Slope of graph is constant &
( R / t)
R0
•As similarly at any temperature
( R / t )
Rt

8. Resistance at Different temperature

9. •Resistance at different temperature
One material has Ro & o
•Resistance at t1 temperature = R t1
Resistance at t2 temperature = Rt2
respectively t1 & t2
If t1,t2, t1, t2 ,(Rt2 or R t1 ) are known
Rt1=Ro[1+ t1t1] Rt2 1+ t2t2
Rt2=Ro[1+ t2t2] Rt1 1+ t1t1

10. For temperature t1 to t2 slope of R t graph
= R / t
=(Rt2 – Rt1) / (t2 –t1)
We know that t1 slope of R t graph
Rt1

11. So t1 (Rt2 – Rt1) / (t2 –t1)
Rt1
So Rt2 = Rt1 [1+ t1(t2-t1)]
• If we know resistance at given temperature
and also know temperature co-efficient at
given temperature so resistance at second
temperature is found by above equation.