Simple Resistance-Temp relationship

[PennStateFan1]

Homework Statement

A copper coil has a resistance of 0.541 Ω at room temperature. What is its resistance when it is cooled to -131.3 °C?

Homework Equations

Ri=New resistance
R0=initial resistance
a=alpha

Ri=R0+R0(a(temp change))
temp change is positive when it goes up

alpha is 4.3E-3 in the book, so that is the right value
Room temp is 20 degC

The Attempt at a Solution

Ri=.541+.541(.0043)(-151.3)
Ri=.189031 ohms

I really feel like I'm doing this right and for all I know the homework program is wrong.

 

[gneill]

Ri=.189031 ohms

I really feel like I'm doing this right and for all I know the homework program is wrong.

Did you enter your result with that many significant figures? The program may be picky about that.

 

[PennStateFan1]

I tried fixing the sigfigs and its still wrong.

 

[Apphysicist]

Looks good, but maybe the program is using a different value for the temperature coefficient of copper? I've seen it more commonly as 0.0039.

 

[PennStateFan1]

It's the right coefficient, because it told what table in the book to use. It's probably the coding for the program. It's a new book we're using and my teacher thinks there might be mistakes.

 

[Dadface]

Look at the the R in your equation(0.541).This is the resistance at 20 degrees.Should it not be the resistance at 0 degrees?

R at 0 degrees=0.541/1+20 alpha
Dont forget that if alpha is referred to R at 0 degrees then the temperature drop is not 151.3

 

[mark_p_n]

Okay, I don't know how late I am to answering your question, but the book I have says that the alpha is 3.9E-3, not 4.3E-3. Everything else is right in your problem because I just did a similar problem to yours in my homework and I got it right. :)