Chapter 32257P32.67From Ampere’s law, the magnetic field at distance rR≤is found as:BrJrIRr202022πµπµbgej==FHGIKJ, or BIrR=022.The magnetic energy per unit length within the wire is thenUBrdrIRrdrIRRIRRA=FHGIKJ=zz200024300244022244416.This is independent of the radius of the wire.P32.68The primary circuit (containing the battery and solenoid) is an RLcircuit with R=14 0. Ω, andLNA××=−−0272441012500100 10007000280A..H.(a)The time for the current to reach 63.2% of the maximum valueis the time constant of the circuit:τ==LR00200200...H14.0 s msΩ.(b)The solenoid’s average back emf isεLfLItLIt=FHGIKJ=−FHGIKJ∆∆∆0FIG. P32.68whereIIVRfFHGIKJ=FHGIKJ=063260 0271...max∆ΩV14.0 A.Thus,L=FHGIKJ=37 9...HA0.020 0 sVaf.(c)The average rate of change of flux through each turn of the overwrapped concentric coil is
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .