The magnitude of the magnetic field in a magnetic resonance imaging (mri) machine can be as great as b = 2.0 t . under normal circumstances, this field cannot be shut off by just flipping a switch. instead the magnitude needs to be carefully decreased to zero. in an emergency, however, the magnet can be "quenched" so that b reduces to zero in 20 s. such a quench can cost thousands of dollars and likely damages the magnets. assume that the magnetic field exists inside a cylinder of radius r = 300 mm and length ℓ = 200 mm . part a how much magnetic potential energy is dissipated when the magnetic field is quenched in this way?