webwork.phys.yorku.ca/ (1 polnt) THE PROBLEM It a blood vessel becomes constrict

Question

webwork.phys.yorku.ca/ (1 polnt) THE PROBLEM It a blood vessel becomes constricted, doctors will somet imes Insert a stent. Suppose a particular stent is a plastic cylnder with metal loops around It. The metal loops allow the stent to be heated and heating avolds growth of new cells that would cause another constriction. Putting the patlent into a changing magnetic field is one way to heat the metal loops Consider a stent with diameter d-4.7 mm. Each metal loop has a resistance of R=40 mS2. The doctors want to provide a heating power of P-244 mw for cach loop. (a) To be most efficient, in what direction should the magnetic field polnt? (b) Calculate the required rate ot change of a magnetic field that is polnting in the most efficient direction. PAPER SOLUTION INTERPRET DEVELOP Derive an algebraic expression tor the rate of change of the magnetic field. dB dt EVALUATE

Explanation / Answer

a) The direction of magnetic field should be perpendicular to the plane of the coil.

b) Induced emf = A*dB/dt

Power dissipated, P = emf^2/R

P*R = emf^2

sqrt(P*R) = emf

sqrt(P*R) = A*dB/dt

==> dB/dt = sqrt(P*R)/A

= sqrt(244*10^-3*40*10^-3)/(pi*0.0047^2/4)

= 5694 T/s

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