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posted by  Hack on 7/24/2008 7:44:22 AM  |  status: Live  

circular loop

Course Textbook Chapter Problem
Calculus Based Physics University Physics with Modern Physics (12th) by Young, Freedman 29 9DQ
Question Details:
A circular loop of flexible iron wire has an initial circumference of 165.0\;{\rm cm}, but its circumference is decreasing at a constant rate of 12.0\;{\rm cm/s} due to a tangential pull on the wire. The loop is in a constant, uniform magnetic field oriented perpendicular to the plane of the loop of magnitude 0.500\;{\rm T}
 
A.
Find the emf induced in the loop, at the instant when 9.0\;{\rm s} have passed.
Express your answer using two significant figures.
 
B.  Is the flow clockwise, or counter clockwise?
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Oracle
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posted by Steve (retired) on 7/24/2008 12:05:04 PM  |  status: Live
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Response Details:
PART A :
 
     circumference of loop = 2*π*r = C
     
     so, area of loop = A = (C/2π)2*π = C2/4π
 
     since area of loop is decreasing, -dC/dt = 0.12 m/s
 
     so, -dA/dt = -C/2π * dC/dt = C/2π * 0.12 m2/s
 
     so, induced emf = -B*dA/dt = 0.500 * C/2π * 0.12 V
 
     = 0.5*(1.65 - 0.12*8)/2π * 0.12 V = 6.589 * 10-3
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Oracle
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posted by Steve (retired) on 7/24/2008 12:05:56 PM  |  status: Live
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Response Details:
LOOKING ALONG THE DIRECTION OF MAGNETIC FIELD, FLUX IS INTO THE LOOP, SO, ACCORDING TO LENZ'S LAW,

CLOCKWISE CURRENT FLOWS IN THE LOOP

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