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Tangent galvanometer 
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#1
May2305, 08:45 PM

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Hey, I was wondering how would you find the value of the magnetic field inside a square coil? My books talk about finding the value of the mag. field at the center of a circular coil and everytime I search google for galvanometers made with square loops, I only find information on circular loops.
In case you're wondering what my class is doing, our teacher wants us to make a lab that he can use for his future students, so my partner and I chose to make a lab that determines the relationship between the current and the angle the compass needle makes with the vertical plane of the coil. Thanks in advance. Syed 


#2
May2305, 09:36 PM

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http://hyperphysics.phyastr.gsu.edu...ic/galvan.html To find the relevant mathematics, do a search for a magnetic dipole. The calculation is easiest for a rectangular coil, but can be generalized to any shape. For example http://www.pa.msu.edu/courses/2000sp...s/dipoles.html http://hyperphysics.phyastr.gsu.edu...ic/magmom.html 


#3
May2405, 12:01 AM

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It is not quite 4 times the field a distance L/2 from a long conducting wire since the sides of the loop are not arbitrarily long. But that is probably a fair approximation. [tex]B = 4\frac{\mu_0I}{2\pi d} = \frac{4\mu_0I}{\pi L}[/tex] where d = L/2[/tex] To get the exact value, you have to do a BiotSavart integration over the length of the 4 sides. AM 


#4
May2405, 10:36 AM

P: 6

Tangent galvanometer
Hey AM, yes this is a tangent galvanometer. The equation you gave me, does that take into account the number of turns in the coil?



#5
May2405, 04:58 PM

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I thought you were trying for find the field everywhere within your rectangular coil. Now I see you really only need it at the center. AM's equation is an approximation because it is the field from four wires of infinite length. Your wires are not infinite, and as he said you would need to do a calculation using the law of BiotSavart to get the correct result for shorter wires. I have found one source that gives the result of that calculation for a wire of finite length at an arbitrary point in the vicinity of the wire. You can use the equation to solve your problem at the center of the coil, and if you want to you can explore the variation in the field as you move a bit away from the center. You will find the equation here: http://www.westbay.ndirect.co.uk/field.htm Click on the link titled "Magnetic Field due to a Current in a Wire". Make sure you use the equation for the short wire, Bsw. Here is another useful link http://www.magson.de/technology/tech41.html It gives the fields anywhere along the axis of a circular or rectangular coil. It also gives the fields for circular or square double coils (Helmholtz coils). As you can see from the pictures here http://physics.kenyon.edu/EarlyAppar...vanometer.html many of these devices use double coils. 


#6
May2505, 02:42 PM

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AM 


#7
May2905, 11:31 PM

P: 6

sup Andrew and Dan, I just wanted to say thank you for all the help, the links were pretty useful and explanatory. Sorry for not responding earlier though as I've been busy with studying for finals lately



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