How to find the radius of copper wire given resistivity values

In summary, the conversation discusses finding the radius of a copper wire using the given data of resistivity and length. However, after attempting the solution, it is discovered that the given resistivity is incorrect and the question itself may be flawed. The conversation ends with a request for the original question to be posted.
  • #1
subopolois
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Homework Statement


i need to find the radius of a copper wire given the following data:
resistivity is 0.25 ohm meter
length of wire is 200 m


Homework Equations


roe=RS/I
roe=resistivity
R= resistance of material
S=cross sectional area
I= length of specimen


The Attempt at a Solution


i was looking at the equation and noticed i don't have any value for the resistance of the copper, so i looked it up online and it said: 0.00000001678 ohm.m. since i have 200m of wire i multiplied it by 200. so into the equation with everything:
0.25=3.356x10^-6 x s/200 meters
rearranging for the cross section area:
s= 21222410.9
although it doesn't say in the question, i assume that the cross section area of copper wire is circular. so i use the area of a circle to find the radius:
A= pi r^2
r= 2599 m

i don't know about you but this doesn't seem right, to have a wire with radius of 2.5 kilometers. I am stuck at what to do, my only guess is that the resistance value is wrong and i know there is and equation for resistance:
resistance= resistivity x length/area
i have the resisivity and the length, but what would i use for area?
help!
 
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  • #2
Yeah, 2.5 km for a radius doesn't make much sense. Neither does the question. The resistivity of copper is not 0.25 ohm*m. It's not even close. And if they give you the bulk resistivity and the length, that's just data, it's not a question. You can't determine radius from that. Can you post the question verbatim?
 

1. How do you calculate the radius of a copper wire using resistivity values?

To calculate the radius of a copper wire, you need to use the resistivity formula which is: resistivity = (resistance * cross-sectional area) / length. You can rearrange this formula to solve for the radius, which would be radius = (resistivity * length) / (resistance * PI). This formula assumes that the cross-sectional area of the wire is circular.

2. What is the resistivity of copper?

The resistivity of copper is approximately 1.68 x 10^-8 ohm-meter. This value can vary slightly depending on the purity and temperature of the copper.

3. What units should I use for the resistivity, length, and resistance values?

The units for resistivity should be in ohm-meter, length should be in meters, and resistance should be in ohms. It is important to use consistent units in the formula to get an accurate result.

4. Can I use this formula for any type of copper wire?

Yes, this formula can be used for any type of copper wire as long as you have the resistivity, length, and resistance values. However, keep in mind that the resistivity of copper may vary slightly depending on the purity and temperature of the wire.

5. Is there an easier way to find the radius of a copper wire?

There are other methods to find the radius of a copper wire, such as using a micrometer or a wire gauge tool. However, using the resistivity formula is a reliable and accurate method as long as you have the necessary values.

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