262 InductanceP32.79(a)BNI==×⋅=×−−µπ0734101 400 2 00120293 10ATmAAmT upwardejbgaf...(b)uB×=⋅FHGIKJ−−20327224103421....TJmNm1 JPa32(c)To produce a downward magnetic field, the surface of the superconductor must carry aclockwise current.(d)The vertical component of the field of the solenoid exerts an inward force on thesuperconductor. The total horizontal force is zero. Over the top end of the solenoid, its fielddiverges and has a radially outward horizontal component. This component exerts upwardforce on the clockwise superconductor current. The total force on the core is upward . Youcan think of it as a force of repulsion between the solenoid with its north end pointing up,and the core, with its north end pointing down.(e)FPA×LNMOQP−−3 42110 101 30 10223.PamNafNote that we have not proven that energy density is pressure. In fact, it is not in some cases;Equation 21.2 shows that the pressure is two-thirds of the translational energy density in an
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