利用楞次定律求感生電流的流動方向。

Q:為什麼用楞次定律可知線圈正進入磁場時，感生電流沿順時鐘方向流動?

A: When the coil PQRS enters into the magnetic field, the flux linkage with the coil increases. Lenz's Law gives that the induced current must flow in a direction so as to oppose the increase of magnetic flux.

As such, the induced current should flow in the clockwise direction. Thus the induced current produces magnetic flux in a direction opposing the given flux.

Q: 線圈包圍的「出紙」磁場線愈來愈多，所以要產生「入紙」的磁場線抗衡，而線圈會受向右的力，利用左手定則怎樣也得不出順時鐘方向，為什麼??

A: You should use Fleming's Right Hand Rule to find the direction of induced current, which would show the same direction as using Lenz's law.

However, if you want to use Fleming's Left Hand Rule, the force given by the induced current should act towards the left, so as to oppose the motion of the coil (which is towards the right). You should find the same current direction.


2015-07-02 16:09:31 補充：
Fleming's Right (or Left) Hand Rule is applying to the section QR of the coil, because this section cuts magnetic field lines when the coil is moving into the field.

2015-07-03 01:10:01 補充：
Q:但是又如何得知感生電流是順時鐘方向流動?
A:Use "Right Hand Grip Rule" (also called "Right Hand Screw Rule").

2015-07-03 01:14:34 補充：
Q:利用左手定則時，力是向左，這一點我明白，但是磁場的方向應該是怎樣，是「出紙」還是「入紙」?
A: Use the given field direction, i.e. pointing out of the paper ( 出紙). Because the induced current in the GIVEN field should produce a force towards the left.

請見:photo.pchome.com.tw/forever2015/143581631378