# college physics

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How to do this problem?

Compute the number of turns of wire on a coil whose resistance measures 15.5 ohms, and which is wound around a 2-inch diameter form in a single layer of 28 gage enameled copper wire.

• college physics -

You get a wire chart out,look up the resistance of #28 copper.
http://www.eskimo.com/~billb/tesla/wire1.txt

• college physics -

I understand. I know you have the formula R = (rho)*length / area.

But how to solve the question? I'm still stuck on it.

• college physics -

No, that is not it. The chart I attached gives for copper 28 wire, the ft/ohm, and other. You know the length is 15.5ohms, determine the length from that table data. Look at the chart.

• college physics -

oh I see. my book has ohns per 1000 feet of copper wire at 25 degrees C.

That should be the data I use but you convert into ft using the ft/ohm data and that should be it? Number of turns?

• college physics -

number turns= length/circumference.

I would put length in inches to match units.

• college physics -

so now at 28 gage wire is listed to be 66.17 ohms per 1000 ft of Copper Wire at 25 degrees C.

Then the coil has 15.5 ohm resistance so 15.5 ohms * (1000 ft / 66.17 ohms) * (12 in / ft) = 2.81 in.

Then we got diameter of 2 inch so 2*pi*1 = 2pi inches for circumference.

Finally, number of turns = length / circumference = 2.81 / 2pi = 0.447?

That sounds odd, what does that mean as an answer IF it is correct?

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