# 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 fourth edition. But that is the same as problem 30 in this fifth edition. I have not gone to the trouble to change all these. ]

More about approximations

and the binomial expansion.

 23.31 23.42 Return to Homework Set

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