Webassign even my ta's didn't know what to do ? and im in intro to physics

Rearrange the second equation to solve for L, then plug into the first equation to solve for A. Once you have A, you can use the equation for the area of a circle (A=\pi r^2) to solve for the radius. Then use that radius to find the diameter. In summary, to find the diameter of a 33 ohm resistor made from a coil of Cu wire with a mass of 12g, use the equations R=\rho \frac{L}{A} and m=dAL to find the length and cross-sectional area of the wire, and then use A=\pi r^2 and the calculated area to find the radius and diameter.
  • #1
phys-lexic
29
0
webassign even my ta's didn't know what to do... ?... and I am in intro to physics

Homework Statement


A 33 ohm resistor is made from a coil of Cu wire whose total mass is 12g. (a)What is the diameter of the wire and (b) how long is it ? ( give you answer in m)



Homework Equations


one equation my ta tried to use was (R) = (resistivity) x (L/A)


The Attempt at a Solution


no idea... we can't figure out where to go because the equation has both length and radius (in the equation for A of the cross section of the wire) as variables... this is the only question left on my webassign and i have 30 mins left... please help
 
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  • #2


There is a mass in the problem. There's a second equation that says mass=density*volume=density*length*area.
 
  • #3


Two equations, two unknowns. Solve:

[tex]R=\rho \frac{L}{A}[/tex] and [tex]m=dV=dAL[/tex] where d is density and rho is resistivity
 

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