Finding rate of magnetic field PLEASE HELP!

  • Thread starter BuBbLeS01
  • Start date
  • #1
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Homework Statement


A 102-turn, 3.8-cm-diameter coil is made of 0.59-mm diameter copper wire. A magnetic field is perpendicular to the coil. At what rate must B increase to induce a 3.4 A current in the coil? The resistivity of copper is 1.7·10-8 Ω·m.


Homework Equations





The Attempt at a Solution


A = (0.00059/2)^2 * pi = 2.734 x 10^-7
I = 3.4 A
I don't what to do???
 

Answers and Replies

  • #2
Is there an answer to compare to at the back of the book?
 
  • #3
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no because its an even number :(
 
  • #4
B=µoNI/2r, B is magnetic force, µo is magnetic constant, N is number of turns, I is current, r is radius

I think that's it but that R is unused in the problem, and it concerns me that I missed something.
 
  • #5
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is r the radius of the coil or th wire??
 
  • #6
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well i did the radius of the coil and its wrong but thanks for trying
 
  • #7
How do you know its wrong?
 
  • #8
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its my homework problem and our homework is on lon-capa....so we have like 4 tries for each problem and tells you when you enter the answer.
 
  • #9
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oh my gosh this problem is driving me nuts I can't figure it out!!! I tried using all sorts of formulas like...
R = pL/A to get the resistance but I don't have L
So then I tried...
B = U*I*(N/L) to get L but I don't have B!!
 
  • #10
hage567
Homework Helper
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Yes you do have L because you know the diameter of the coil and how many turns there are.
 
  • #11
Isn't the L for B=UIN/L the length of the solenoid not the length of the wire?
 
  • #12
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oh yea...ugh I hate this problem!!!
 
  • #13
hage567
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Isn't the L for B=UIN/L the length of the solenoid not the length of the wire?

I was referring to the L in the resistivity equation that Bubbles was asking about.
 
  • #14
I was referring to the L in the resistivity equation that Bubbles was asking about.

Oh I see. What's the step after finding R?
 
  • #15
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How do I find L with having the diameter and number of turns??
 
  • #16
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I was going to find E using I = E/R then use that in the equation...
E = A * B/t to get the rate
 
  • #17
How do I find L with having the diameter and number of turns??

Well, circumference=pi*diameter, lol 102 turns = 102 circumferences
 
  • #18
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oh lol....ok so my length is 9.8696 the when I use R = pL/A is it the area of the wire or coil??
 
  • #19
hage567
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I was going to find E using I = E/R then use that in the equation...
E = A * B/t to get the rate

This is what I would try.
 
  • #20
hage567
Homework Helper
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oh lol....ok so my length is 9.8696 the when I use R = pL/A is it the area of the wire or coil??

The wire, since that is what you are finding the resistance of.
 
  • #21
oh lol....ok so my length is 9.8696 the when I use R = pL/A is it the area of the wire or coil??

Area of wire, cross section area.
 
  • #22
hage567
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Isn't the L for B=UIN/L the length of the solenoid not the length of the wire?

The question did not actually state that this was a solenoid. It said it was a loop of 102 turns with a magnetic field perpendicular to it (so going through it). The magnetic field is not being produced by the coil. So I don't think the B = U*I*(N/L) equation is what you are looking for here, IMO.
 
  • #23
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and the length would be the length of the wire not the coil right
 
  • #24
hage567
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Yes, that's right.
 
  • #25
The question did not actually state that this was a solenoid. It said it was a loop of 102 turns with a magnetic field perpendicular to it (so going through it). The magnetic field is not being produced by the coil. So I don't think the B = U*I*(N/L) equation is what you are looking for here, IMO.

Oh I see. Thanks for setting me straight. I'm still learning and your opinion is very helpful to me.
 

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