If an electric current is passed through this wire, which direction will the wire be pushed (by the interaction of the magnetic fields)?
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Is this an example of an electricmotor或电动发电机?
The wire will be pushedupin thismotorexample.
A visual aid to understanding the interaction of the two magnetic fields is a diagram showing the lines of flux emanating from the permanent magnets, against the circular lines of flux around the wire. Ask those students who came across similar illustrations in their research to draw a picture of this on the board in front of the class, for those who have not seen it.
If this wire (between the magnet poles) is moved in an upward direction, what polarity of voltage will the meter indicate?
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Describe the factors influencing the magnitude of the voltage induced by motion, and determine whether this is an example of an electricmotor或电动发电机.
If this wire (between the magnet poles) is moved in an upward direction, and the wire ends are connected to a resistive load, which way will current go through the wire?
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We know that current moving through a wire will create a magnetic field, and that this magnetic field will produce a reaction force against the static magnetic fields coming from the two permanent magnets. Which direction will this reaction force push the current-carrying wire? How does the direction of this force relate to the direction of the wire’s motion? Does this phenomenon relate to any principle of electromagnetism you’ve learned so far?
The reaction force will be directly opposed to the direction of motion, as described by Lenz’s Law.
Follow-up question: What does this phenomenon indicate to us about the ease of moving a generator mechanism under load, versus unloaded? What effect does placing an electrical load on the output terminals of a generator have on the mechanical effort needed to turn the generator?
If you happen to have a large, permanent magnet DC motor available in your classroom, you may easily demonstrate this principle for your students. Just have them spin the shaft of the motor (generator) with their hands, with the power terminals open versus shorted together. Your students will notice a huge difference in the ease of turning between these two states.
After your students have had the opportunity to discuss this phenomenon and/or experience it themselves, ask them why electromechanical meter movement manufacturers usually ship meters with a shorting wire connecting the two meter terminals together. In what way does a PMMC meter movement resemble an electric generator? How does shorting the terminals together help to protect against damage from physical vibration during shipping?
要求您的学生描述哪些因素影响这种反作用力的大小。
确定诱导电压之间的极性，因为该线环的末端在两个磁体之间旋转：
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Challenge question: if a resistor were connected between the ends of this wire loop, would it “see” direct current (DC), or alternating current (AC)?
请注意，随着循环旋转，两根线端开关极性。要求您的学生解释为什么两极分化。
Describe the nature of the voltage induced in the stationary (“stator”) windings, as the permanent magnet rotor rotates in this machine:
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What factors determine the magnitude of this voltage? According to Faraday’s Law, what factors can we alter to increase the voltage output by this generator?
Is the induced voltage AC or DC? How can you tell?
Increase the [(dφ)/dt] rate of change, or increase the number of turns in the stator winding, to increase the magnitude of the AC voltage generated by this machine.
Follow-up question: AC generators, or交流发电机有时被称为，通常是在适当条件下操作时长寿命的机器。但是像所有机器一样，它们最终将失败。根据问题中给出的说明，确定交流发电机的一些可能的故障模式，以及哪些条件可能会加速此类失败。
Ask your students to write the equation for Faraday’s Law on the whiteboard, and then analyze it in a qualitative sense (with variables increasing or decreasing in value) to validate the answers.
为了使学生思考，对这个问题的第一个答案（增加[（dφ）/dt]）是有目的地含糊不清的。具体来说，必须更改什么才能随着时间的推移提高这种变化的速度？生产发生器后，哪些现实世界变量可变，哪些不是？
In order to make the most practical AC generator (oralternator, as it is also known), which design makes more sense: a stationarypermanent magnet带有旋转的线圈，或带有固定电线线圈的旋转永久磁铁？解释您的选择。
It is more practical by far to build an alternator with a stationary wire coil and a rotating magnet than to build one with a stationary magnet and a rotating wire coil, because a machine with a rotating coil would require some form ofbrushes和slip ringsto conduct power from the rotating shaft to the load.
Follow-up question: what is so bad about brushes and slip rings that we want to avoid them in alternator design if possible?
回答后续问题可能需要对学生进行一些研究。要求他们描述什么是“刷子”以及什么是“滑环”，然后这些部分的机械磨损方面应该变得朴素。
我们知道，为了在线圈中诱导正弦电压，将线圈转弯连接起来的磁通量必须随时间沿正弦路径沿着一条正弦路径，相移90ofrom the voltage waveform. This relationship between flux and induced voltage is expressed in Faraday’s equation v = N [(dφ)/dt]:
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Based on this fact, draw the position of the magnetic rotor in this alternator when the voltage is at one of its peaks:
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The alternator voltage peaks when the magnetic flux is at the zero-crossover point:
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(The actual magnet polarities are not essential to the answer. Without knowing which way the coils were wound and which way the rotor is spinning, it is impossible to specify an exact magnetic polarity, so if your answer had “N” facing down and “S” facing up, it’s still acceptable.)
这个问题挑战学生将磁通波形（φ）与瞬时转子位置联系起来。答案可能会让某些人感到惊讶，他们期望转子与定子杆连接时发生最大感应电压。但是，这个答案将随着时间的流逝将通量（φ）与流量变化率混淆的错误（[（（dφ）/dt]））。与定子杆衬的转子会导致通过这些杆的最大通量（φ），但不会随着时间的推移（[（Dφ）/dt]）。
If this alternator is spun at 4500 RPM (revolutions per minute), what will be the frequency of its output voltage?
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提示：每次转子的革命都会产生多少个AC周期？
f = 75 Hz
学生应该意识到，转子轴的每一次革命都会产生一个交流电压周期。从那时起，问题只是单位转换的问题。
How fast must a 12-pole alternator spin in order to produce 60 Hz AC power? Write a mathematical equation solving for speed (S) in terms of frequency (f) and the number of poles (N).
s =600 RPM, for f = 60 Hz.
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Follow-up question: algebraically manipulate this equation to solve for the number of poles (N) needed in a generator given speed (S) and frequency (f).
这可能会使某些学生尤其令人困惑，直到他们意识到交流发电机极是2的倍数（最简单的交流发电机，具有2个极点）。
如果交流发电机以6000 rpm的轴速度产生400 Hz功率，则有多少杆？
8杆，与4杆相同pairs.
Follow-up question: algebraically manipulate the speed/poles/frequency equation to solve for the frequency generated (f) given the number of poles (N) and the generator speed (S).
Some references provide equations in terms ofpole pairsinstead of individual alternator poles.
假设交流发电机的输出频率必须保持恒定（在国家电力系统中，所有电厂的频率必须相同），如何调节其输出电压？换句话说，由于我们没有增加或降低其旋转速度控制电压的奢侈品，因为这会改变频率，所以我们如何哄骗交流发电机以或多或少的需求产生或多或少的电压？
提示：汽车交流发电机的制造具有此功能，尽管该应用程序的目的是尽管发动机速度变化，但该应用程序的目的是保持恒定电压。在汽车电气系统中，交流发电机的输出的频率无关紧要，因为AC被“纠正”到DC（频率= 0 Hz）中以给电池充电。
The rotor cannot be a permanent magnet, but must be an electromagnet, where we can change itsmagnetic fieldstrength at will.
Follow-up question: how is it possible to conduct electric power to windings on a spinning rotor? Should we energize the rotor winding with AC or DC? Explain your answer.
Ask your students how this voltage regulation strategy compares with that of DC generators. Ask them to describe the difference between “commutator bars” and “slip rings.”
假设我们有一个交流发电机与两组获胜dings,A和B:
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Each pair of windings in each set is series-connected, so they act as just two separate windings:
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如果每个绕组对的一端连接在一个共同的接地点，并且每个绕组对输出70伏RMS，则在开放绕组对端之间测量多少电压？
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99 volts
Hint: if you don’t understand how this voltage value was calculated, plot the voltage output of the two windings as if they were shown on an oscilloscope. Thephase relationship在两个电压之间是解决方案的关键。
Follow-up question: draw a phasor diagram showing how the difference in potential (voltage) between the wire ends is equal to 99 volts, when each winding coil’s voltage is 70 volts.
这个问题是在非常实用的背景下，很好地练习学生对相位转移的了解。
Suppose we have an alternator with three sets of windings,A,B， 和C:
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每组中的每对绕组都是串联连接的，因此它们仅充当三个单独的绕组（请密切注意相标记的点！）：）：
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如果每个绕组对的一端连接在一个公共接地点，并且每个绕组对输出70伏RMS，则在任何两个开机线之间都可以测量多少电压？
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121.2 volts
后续问题：绘制一个相图图，显示导线端之间的电势差（电压）等于121.2伏，当每个绕组线圈的电压为70伏时。
这个问题是在非常实用的背景下，很好地练习学生对相位转移的了解。
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