23.2 Faraday's Law of Induction: Lenz's Law
An MRI technician moves his hand from a region of very low magnetic field
strength into an MRI scanner's 2.01 T field with his fingers pointing in the
direction of the field.
a) Find the average emf induced in his wedding ring, given its diameter is 2.21 cm
and assuming it takes 0.252 s to move it into the field.
mV
b) What current is induced in the ring if its resistance is 0.0097 ??
A
c) What average power is dissipated?
mW
d) What magnetic field is induced at the center of the ring?
T
What are the directions of the induced magnetic field and current, respectively,
relative to the MRI's field?
A. Into MRI, clockwise
B. Out of MRI, counterclockwise
C. Into MRI, counterclockwise
D. Out of MRI, clockwise
Hint: for part d, to calculate induced magnetic field, remember the formula for
magnetic field at the centre for a wire loop (ring in this case) due to current flowing
through it - magnetism chapter.
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