The Heating of Nichrome Wire in a toaster

[gc33550]

Homework Statement

A toaster with a Nichrome heating element has a resistance of 70 ohms at 20^oC and an initial current of 1.6 A. When the heating element reaches its final temperature, the current is 1.39 A. What is the final temperature of the heating element?

Homework Equations

V=IR
$$\alpha$$=($$\rho$$-$$\rho$$_o)/$$\rho$$/(T_f-T_o)

The Attempt at a Solution

I know that the voltage will remain constant therefore:
I_o*R_o=I_f*R_f
I also know that Nichrome's $$\alpha$$=100e-8
but I don't really know where to go from here

 

[willem2]

from $$<br /> \alpha = \frac {\rho - \rho_0} {\rho} (T_f - T_0) <br />$$

try to derive an equation for R as a function of R_0, T_0, T_f and $\alpha$
you know the new R from ohms law.

The temperature coefficient of nichrome is $4 *10^{-4} K^{-1}$

 

[gc33550]

So am I going to be looking at resistivity then? such as $$\rho$$=R*A/L ??

 

[willem2]

So am I going to be looking at resistivity then? such as $$\rho$$=R*A/L ??

yes. Instead of $$\rho$$=R*A/L you can use $$\rho$$=R*C. You don't know what A and L are anyway, except that they are constant.

 

[gc33550]

C as in capacitance? How do I find that?

 

[willem2]

C as in capacitance? How do I find that?

no it's just an arbitrary constant

 

[gc33550]

would that constant be in my physics book somewhere?