A generator is constructed by rotating a coil of N turns in

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A generator is constructed by rotating a coil of N turns in a magnetic field B at a frequency f.The internal resistance of the coil is R and the cross sectional area of the coil is A.
Which of the following statements are true?(Give ALL correct answers,i.e.,B,AC,BCD...)
A) The amplitude of the induced EMF doubles if the frequency f is doubled.
B) The amplitude of the induced EMF doubles if the magnetic field B is doubled.
C) The amplitude of the induced EMF doubles if the resistance R is doubled.
D) The maximum induced EMF occurs when the coil is rotated about an axis parallel to the magnetic field lines.
E) The amplitude of the induced EMF doubles if the area A is doubled.
F) The maximum induced EMF occurs when the coil is rotated about the axis of the coil.

对于本问题
感生电动势 ε = B A (2πf) cos(2πf t)
其中 π 是圆周率,t 是时间.以线圈平面平行于磁力线时作为时间零点.
因此
A B E 都是正确的
C 是错误的,内阻R 增大,感生电动势不变,感生电流减小
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对于通常的交流发电机,线圈的转动轴是于磁力线垂直的,根本就不存在 "rotates about an axis parallel to the magnetic field lines" 的可能性,除非是错误安装的发电机.但题目却出现了这个选择项目D,很怪异.
正常的发电机,感生电动势的最大值发生在线圈平面与磁力线平行的时刻.
而如果线圈是绕平行于磁力线的轴转动的话,那么通过线圈截面的磁通量始终为0,根本就不会产生感生电动势.
F 选择项也很怪异."axis of the coil" 线圈的轴表达不明确.按常理,应该是与线圈平面垂直的轴.但是如果绕这个轴转的话,也不会产生磁通量的变化.
综上所述,我认为选择 A B E

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