Good afternoon, I have the following problem, i know : l=x (to be solved), d=0.5mm, and R=1ohm, and rho (ohm/meter) ie the Resistivity is 2.5e-8. I have a formula and have rewritten it to read, l=(RA)/p. When i solve i get my answer to be 7.85e-16 but the answer is supposedly 785.39m, what am i doing wrong or is the book wrong?

Question

anonymous · Answer

$$l=RA \div \rho$$

anonymous · Answer

In 2.5e-8 is it Capital E or small e only

anonymous · Answer

as is in 2.5*10^-8 sorry if it was unclear :) thanks

anonymous · Answer

$$2.5\times10^{-8}$$

anonymous · Answer

Hope you got the answer

anonymous · Answer

so did you get the same answer then? Thanks

anonymous · Answer

I got 7.85m

anonymous · Answer

hmmm could you walk me through what you did to get that please?

anonymous · Answer

attachment

anonymous · Answer

Hope you understood the problem.

anonymous · Answer

Thank You sooooooo much!

anonymous · Answer

I now see whre i went wrong was on my conversion between mm-metres on the diameter and Area bit. Thanks again for the help Gautman, and i hope you have a great day!

anonymous · Answer

You are welcome.

anonymous · Answer

You need to convert the diameter into meters then halve that to get radius, then use pi r^2 for the cross sectional area.  Then you get the A value to be (0.00025^2 x pi) = 1.96 ^-7 m^2.  Use that in your equation.