07al physics mc

2011-04-17 2:30 am

一條均勻的重繩自由地掛在一支持點上。現使支持點作細小振幅的水平振盪。
由此產生沿繩向下傳播的橫波，並在自由端反射形成駐波。

為什麼繩上每一振動點的振盪頻率都相同？
節點不是沒頻率嗎？

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用恆定電壓的直流電源驅動電動機以偉起負荷。如增加負荷，
電樞線圈的轉速
電樞線圈的電流
電樞線圈的中的反電動勢
會增加減少不變？

我想問，為什麼？
轉速減少，反電勢應該減少才對！不懂...

回答 (1)

天同

2011-04-17 6:48 pm

✔ 最佳答案

I don't have the orignal questions in hand, and could only give answers based from what you have written.

Q: 為什麼繩上每一振動點的振盪頻率都相同？節點不是沒頻率嗎？

You are asked the frequency of vibration of each "vibration point" (振動點). A node (節點) is indeed NOT a "vibration point". It is thus irrelevant to the question.

Q:電樞線圈的轉速,電樞線圈的電流, 電樞線圈的中的反電動勢
會增加減少不變？

Assume the motor is ideal. the rotation speed (轉速) would decrease; the current (電流) would increase; and the back emf ( 反電動勢) would decrease.

Q: 轉速減少，反電勢應該減少才對！不懂...

A lower rotational speed leads to a less flux change in a unit time. Thus the (back) induced emf would decrease.

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