# please help - resistance question?

Discussion in 'Homework Help' started by 115, Apr 21, 2008.

1. ### 115 Thread Starter New Member

Apr 21, 2008
3
0
What is the total resistance, at 273°K, of a copper conductor of cross sectional area 10mm2 and length 1000m.

Hi i'm new on here and struggling with the above question can anyone help?!

2. ### Caveman Active Member

Apr 15, 2008
471
0
Resistance(Ohms) = Resistivity(Ohm-m) * length(m) / cross-sectional area(m^2).
You just need the resistivity of copper at 273 degrees K.

3. ### 115 Thread Starter New Member

Apr 21, 2008
3
0
i think its 0.004 ohm/ohm°C

4. ### Caveman Active Member

Apr 15, 2008
471
0
Okay, I found it.
The resistivity of copper at 20deg C is 16.78nOhm-m.
And the resistivity of copper increases at 0.393 percent per degree C.
So, the resistivity at 273 Kelvin = 0 degrees C is
16.78nOhm-m*(1-0.00393*20) = 15.461092nOhm-m

And your final answer is:
Resistance(nOhms) = 15.461092nOhm-m * 1000m / 10e-6m^2 = 1546109200nOhms = 1.5461092 Ohms.

Now just to reassure myself, I looked in standard copper wire resistance tables. 10mm^2 is between the 8AWG and 6AWG. The resistance of 1000m of 8 and 6AWG is 2.1Ohms and 1.32Ohms, respectively. So, this works.

5. ### 115 Thread Starter New Member

Apr 21, 2008
3
0
thankyou so much thats a great help.