感生電流的正負電流?!

http://sciedu.cc.nctu.edu.tw/practice/threehair/page_1.htm
http://www.hk-phy.org/resources/ppt/ele5/ppframe.htm



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2008-09-15 21:12:06 補充：
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This is due to cutting of field lines by the coil of the solenoid.

There are magnetic filed lines surrounding a bar magnet. When the magnet is pushed into a solenoid, the field lines associated with the magent is being cut by each coil of the solenoid. This causes current to flow in the coils in one direction (the process is electromagnetic induction).

When the magnet is withdrawn from the solenoid, the field lines of the magnet are again cut by the coils. But this time, the relative motion of the field lines and coils is reversed. The current induced is reversed.

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