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Magnetic field strength dependent on distance from source

by babemagnetics
Tags: dependent, distance, field, magnetic, source, strength
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jtbell
#19
Feb22-13, 06:09 AM
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See here for the magnetic field along the axis of a finite solenoid:

http://www.phys.uri.edu/~gerhard/PHY204/tsl215.pdf

This assumes the solenoid has no iron or other magnetic material inside it.
mrv11
#20
Aug1-13, 01:13 PM
P: 2
Thank you all for the help on this little project!

I have to apologize about the delay for my thanks. School became overwhelming so I had to put this on hold. I reviewed the info you all provided, along with a great text a professor lent me. While not one of those individual sources described exactly my situation, I was able to synthesize it all into a decent model to describe my data.

Thanks again!
downtownjapan
#21
May16-14, 10:19 AM
P: 6
Hi everyone,

I am trying to use the 1/r^3 formula to calculate the decrease in magnetic field strength over distance, but I must be doing something very, very wrong following this formula because the numbers I get don't make sense to me. I have clearly made a mistake applying the formula and I am wondering if someone could tell me where I have gone wrong.

I am trying to calculate how a field of 0.005 Tesla will decrease at a distance of 0.0005 meters away.

I have done the following calculation
0.005T/0.0005^3 meters, which gives me the number
0.005/0.0005^3 = 40,000,000

Obviously I have gone horribly wrong, and I have a feeling I am making a very basic mistake somewhere with either the calculations and/or the understanding of the formula. If any kind-hearted charitable soul out there wants to tell me how this poor fool has gone wrong, I would be very grateful!
Philip Wood
#22
May16-14, 11:23 AM
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P: 963
Quote Quote by downtownjapan View Post
I am trying to calculate how a field of 0.005 Tesla will decrease at a distance of 0.0005 meters away.
Away from where? You need to sort out from where your distances are measured… We need to know the set-up.
mfb
#23
May16-14, 03:04 PM
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P: 12,053
Quote Quote by downtownjapan View Post
Hi everyone,

I am trying to use the 1/r^3 formula to calculate the decrease in magnetic field strength over distance, but I must be doing something very, very wrong following this formula because the numbers I get don't make sense to me. I have clearly made a mistake applying the formula and I am wondering if someone could tell me where I have gone wrong.

I am trying to calculate how a field of 0.005 Tesla will decrease at a distance of 0.0005 meters away.

I have done the following calculation
0.005T/0.0005^3 meters, which gives me the number
0.005/0.0005^3 = 40,000,000

Obviously I have gone horribly wrong, and I have a feeling I am making a very basic mistake somewhere with either the calculations and/or the understanding of the formula. If any kind-hearted charitable soul out there wants to tell me how this poor fool has gone wrong, I would be very grateful!
A simple way to see why your answer is wrong: work with units. Your calculation gives 40000000 T/m3 - this has the wrong units for a magnetic field strength. And the numeric value depends on the length units you use.

Those 40000000T would be the magnetic field at this distance if you had a point-like source that has a field of 0.005 T in a distance of 1m. Such a source is completely unrealistic.

By the way: please start a new thread if other threads are several months old.


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