12.07.2015 Views

Simple Nature - Light and Matter

Simple Nature - Light and Matter

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(f) Use conservation of energy to relate your answers from parts c,√d, <strong>and</strong> e, <strong>and</strong> solve for a.54 Magnet coils are often wrapped in multiple layers. Thefigure shows the special case where the layers are all confined to asingle plane, forming a spiral. Since the thickness of the wires (plustheir insulation) is fixed, the spiral that results is a mathematicaltype known as an Archimedean spiral, in which the turns are evenlyspaced. The equation of the spiral is r = wθ, where w is a constant.For a spiral that starts from r = a <strong>and</strong> ends at r = b, show that thefield at the center is given by (kI/c 2 w) ln b/a.⊲ Solution, p. 939Problem 54.Key to symbols:easy typical challenging difficult very difficult√An answer check is available at www.light<strong>and</strong>matter.com.730 Chapter 11 Electromagnetism

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