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.
You get a wire chart out,look up the resistance of #28 copper.
http://www.eskimo.com/~billb/tesla/wire1.txt
I understand. I know you have the formula R = (rho)*length / area.
But how to solve the question? I'm still stuck on it.
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.
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?
number turns= length/circumference.
I would put length in inches to match units.
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?
To compute the number of turns of wire on the coil, you need to gather some information and apply a few formulas. Here's how you can approach the problem step-by-step:
1. Find the length of the wire:
- Determine the circumference of the coil's form using the diameter given. Remember, the formula for circumference is C = π * d, where C is the circumference and d is the diameter.
- Since the diameter is given in inches, convert it to centimeters (if necessary) for consistency.
- Multiply the circumference by the number of turns in the coil to find the total length of wire used.
2. Find the resistance per unit length:
- The resistance per unit length of a wire can be calculated using the formula R = (ρ * L) / A, where R is the resistance, ρ is the resistivity of copper, L is the length, and A is the cross-sectional area.
- For copper, the resistivity (ρ) is a constant value, which you can look up or find in reference material.
- Since the wire is enameled, the wire's insulation thickness needs to be taken into account when calculating the cross-sectional area. You may need to refer to a reference material to find the equivalent diameter.
3. Solve for the number of turns:
- Rearrange the formula from step 2 to solve for the length (L = (R * A) / ρ).
- Substitute the resistance, resistivity, and cross-sectional area values obtained from the problem into the rearranged formula.
- Divide the total length of wire used obtained in step 1 by the length per turn obtained in the previous step to get the number of turns.
By following the steps above and performing the necessary calculations, you should be able to find the number of turns of wire on the coil.