University Physics Young and Freedman Chapter 28 Concept Questions and solutions Chapter 28: Pre-Chapter Question Q: If the diameter of one of the MRI coils is increased without changing the current, does the magnetic field that it produces at its center increase, decrease, or stay the same? A: From Eq. 28.17, increasing the diameter and hence the radius a causes the magnetic field to decrease. A large diameter means tehre are more moving charges to produce a magnetic field; it also means that the field point at the center of the coil is farther from those charges. In this case the latter of these factors is more important, so Bx decreases with increasing diameter. 1. If two protons are traveling parallel to each other in the same direction and at the same speed, is the magnetic force between them attractive or repulsive? What about the net force between them? (Assume the protons' speed is far less than the speed of light.) The magnetic force is attractive because the direction of the magnetic force on the upper
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This note was uploaded on 04/18/2008 for the course PHYS 0030 taught by Professor Cutts during the Spring '07 term at Brown.