William H. Hayt and John. A. Buck, Engineering Electromagnetics. McGraw-Hill, ver 7, 2006.
저작시기 2006.07 |등록일 2008.03.14
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3.1. An empty metal paint can is placed on a marble table, the lid is removed, and both parts are
discharged (honorably) by touching them to ground. An insulating nylon thread is glued to
the center of the lid, and a penny, a nickel, and a dime are glued to the thread so that they
are not touching each other. The penny is given a charge of +5 nC, and the nickel and dime
are discharged. The assembly is lowered into the can so that the coins hang clear of all walls,
and the lid is secured. The outside of the can is again touched momentarily to ground. The
device is carefully disassembled with insulating gloves and tools.
a) What charges are found on each of the five metallic pieces? All coins were insulated
during the entire procedure, so they will retain their original charges: Penny: +5nC;
nickel: 0; dime: 0. The penny’s charge will have induced an equal and opposite negative
charge (-5 nC) on the inside wall of the can and lid. This left a charge layer of +5 nC on
the outside surface which was neutralized by the ground connection. Therefore, the can
retained a net charge of −5nC after disassembly.
b) If the penny had been given a charge of +5 nC, the dime a charge of −2 nC, and the nickel