Ch23 Homework Solutions

23.30.Example 23.9 derives the exact expression for the electric field at a point on the axis of a uniformly charged disk. Consider a disk of radius R = 3.0 cm = 0.03 m, having a uniformly distributed charge of + 5.2 microCoulombs.

(a) Using the result of Example 23.9, compute the electric field at a point on the axis and 3.0 mm (0.003 m) from the center. Compare this answer with the field computed from the near-filed approximation.

(b) Using the result of Example 23.9, compute the electric field at a point on the axis and 30 cm (0.30 m) from the center. Compare this answer with the field obtained be treating the disk as a + 5.2 microCoulomb point charge at a distance of 30 cm.[ These solutions say "23.35" because this was problem 35 in Serway's

fourthedition. But that is the same as problem30in thisfifthedition. I havenotgone to the trouble tochangeall these. ]

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