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Magnetism - Quick solenoid question

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


A 200-turn solenoid having a length of 25cm and a diameter of 10cm carries a current of 0.29A. Calculate the magnitude of the magnetic field B inside the solenoid.


Homework Equations


B = [tex]\mu[/tex]0ni


The Attempt at a Solution


Well, I plugged the numbers into the equation and got 7.28x10^-5 T as the answer. However, this is wrong. The correct answer is meant to be 0.3 mT. I can't see where I've gone wrong because the magnetic field inside a solenoid is meant to be independent of its dimensions, right?

EDIT: I found the number of turns per unit length, then put that into the equation and still get the wrong answer. I'm confused.

B = 4[tex]\pi[/tex]x10-7 Tm/A x (200/0.25) x 7.5A = 7.28x10^-5.

I've no idea why I get that. Maybe the diameter has some significance that I haven't managed to see yet.
 
Last edited:

Answers and Replies

  • #2
Doc Al
Mentor
44,882
1,129
Show exactly what you plugged in for each factor.
 
  • #3
Doc Al
Mentor
44,882
1,129
A 200-turn solenoid having a length of 25cm and a diameter of 10cm carries a current of 0.29A.
...
B = 4[tex]\pi[/tex]x10-7 Tm/A x (200/0.25) x 7.5A = 7.28x10^-5.
Looks to me like you are using the wrong current.
 
  • #4
15
0
Oops. I apologise for wasting time. I used a current from a different question by accident :).
 

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