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Old May 16th 2009, 09:32 PM   #1
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Coil-Magnetism Problems

1. A wire is bent in the form of a square of side 20cm. It carries a current of 2A. Find the magnetic field at the center of the square.

2. A coil of area 20 cm² is placed so that a magnetic field of 0.1 T is perpendicular to the plane of the coil. If the coil is turned through 180° in 0.1 seconds, find the emf induced.

I don't seem to make head or tail of either questions. If the first one were in the form of a circular loop, the question would be easy. The second one boggles my mind more.

Last edited by SVXX; May 16th 2009 at 09:35 PM.
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Old May 16th 2009, 10:19 PM   #2
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(1)The magnetic field due to a straight current carrying wire at a point on its perpendicular bisector is given by- (please see attachment)

B ={UoI/(4IId)}*(cos@1 - Cos@2), where Uo stands for mu-not and II stands for pi)

Put Io/4II = 10^-7, d = 10cm = 0.1 m, @1=45 and @2 = 135 degree.

The field due to four sides will be four times of the above value and will be directed inward.
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Old May 16th 2009, 10:27 PM   #3
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(2) Let the area of the coil be A and the magnetic field be B then the flux linked with the coil = BAcos@ = BA as @ = 0

Let the coil is turned through 180 degre in time t, the flux linked now will be BAcos180 = -BA

Change in flux = -BA -Ba = -2BA and the magnitude of the change influx will be 2BA

Induced emf = rate of change of flux = 2BA/t = (2*0.1*20*10^-4)/0.1 volt
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Old May 16th 2009, 10:51 PM   #4
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Sorry. The attachment referred to in question (1) is here.

Last edited by Parvez; Jun 3rd 2009 at 08:52 AM.
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Old May 16th 2009, 10:55 PM   #5
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Sorry. The attachment referred to in question (1) is here.

Sorry again. I attached a different file. The correct one is attached again.

Last edited by Parvez; Jun 3rd 2009 at 08:52 AM.
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