Physics Help Forum Coil-Magnetism Problems

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 May 16th 2009, 10:32 PM #1 Junior Member   Join Date: May 2009 Posts: 4 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 10:35 PM.
 May 16th 2009, 11:19 PM #2 Physics Team   Join Date: Feb 2009 Location: India Posts: 365 (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.
 May 16th 2009, 11:27 PM #3 Physics Team   Join Date: Feb 2009 Location: India Posts: 365 (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
 May 16th 2009, 11:51 PM #4 Physics Team   Join Date: Feb 2009 Location: India Posts: 365 Sorry. The attachment referred to in question (1) is here. Last edited by Parvez; Jun 3rd 2009 at 09:52 AM.
 May 16th 2009, 11:55 PM #5 Physics Team   Join Date: Feb 2009 Location: India Posts: 365 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 09:52 AM.