Help I am stuck! resistivity/resistance question.....?

Question

Hi again - I'm sorry I didn't understand the answer that someone posted half an hour ago. From the answer I am getting nowherenear 6.492?

Hi can anyone help me out with physics homework?

I need to find out the resistance of 0.31 mm diameter constantan wire. Constantan wire has a resistivity of 49 x 10-8 and the length is 1000mm.

The second question is as above but with a length of 500mm.

I have the equation of r = pL/A but I keep getting different answers not sure what I am doing?

Is it 49 x 1(for a metre) / pi x (0.31/2) squared?
Can you help me out? I dont know what I am doing!

Thank you

J

Answer 1

What's the problem? You gave the whole answer. The only thing is that you need to work this through in meters, not mm.

4.9e-8/(3.14159x(0.31E-3/2)^2)
= 6.4921

Half the length has half the resistance.

3.246

Answer 2

resistance = (rho*length)/(pass sectional section) or R = pl/A. For the 1st section you answer may be: R = ((40 9 x 10^-8)(a thousand x 10^-3))/(pi(.00031/2)^2) = 6.492 Ohms merely replace the a thousand interior the 1st section to 500 interior the 2d. perhaps you forgot to be sure each little thing replace into in meters.