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国際バカロレア · IB Diploma · Physics · HL トピック 19 4:09 英語ナレーション・英語＋中文字幕 burning-in
章
Transcript
A magnet beside a wire does not always produce a current.
磁铁靠近导线并不总是产生电流。
An induced electromotive force depends on changing magnetic flux linkage.
感应电动势取决于磁通链的变化。
A field describes a force effect at positions in space.
场描述空间中各位置的力效应。
A current-carrying conductor in a magnetic field can experience a force.
载流导体在磁场中可能受到力的作用。
Electromagnetic induction occurs when magnetic flux linkage changes.
电磁感应发生在磁链变化时。
Induction is the creation of emf by changing flux linkage.
感应是指通过改变磁链产生电动势的过程。
A transformer is a device transferring energy between coils through changing flux.
变压器是一种通过改变磁链在线圈之间传递能量的装置。
Changing field strength, coil area, orientation, or relative motion can change flux linkage.
改变场强、线圈面积、方向或相对运动均可改变磁通链。
Lenz law describes an induced effect opposing the change producing it, consistent with energy conservation.
楞次定律描述了一种感应效应，该效应阻碍产生它的变化，这与能量守恒定律一致。
In the lab: Use a coil and sensitive meter to compare magnet motion in each direction.
在实验室中，使用线圈和灵敏电表比较磁铁在各方向上的运动。
Record that a stationary arrangement gives no induced signal.
记录表明，静止排列不会产生感应信号。
Use approved low-voltage supplies for motor demonstrations.
电机演示请使用经批准的低压电源。
Known: a transformer has 200 primary turns, 50 secondary turns and 12 V primary voltage.
已知：一个变压器有200个初级线圈匝数，50个次级线圈匝数和12 V初级电压。
For an ideal transformer, Vs divided by Vp equals Ns divided by Np.
对于理想变压器，Vs除以Vp等于Ns除以Np。
Vs equals Vp times Ns divided by Np, which is 12 times 50 divided by 200, equaling 3.0 V.
Vs等于Vp乘以Ns除以Np，即12乘以50除以200，等于3.0 V。
Real transformers also dissipate energy.
实际变压器也会耗散能量。
Your turn.
轮到你了。
An ideal transformer has N p equal to 400, N s equal to 100 and V p equal to 20 volts.
一个理想变压器的原线圈匝数 Np 等于 400，副线圈匝数 Ns 等于 100，原线圈电压 Vp 等于 20 伏特。
Find V s.
求副线圈电压 Vs。
A transformer needs a changing magnetic flux.
变压器需要变化的磁通量。
A steady DC input does not provide continuous transformer action.
稳定的直流输入无法提供持续的变压器作用。
Magnetic field direction is not automatically the direction of force.
磁场方向并不自动等同于受力方向。
Not true: A steady DC input produces continuous ideal transformer action.
不正确。 稳定的直流输入无法产生持续的理想变压器作用。
A transformer works by electromagnetic induction, which requires changing flux.
变压器依靠电磁感应工作，而电磁感应需要变化的磁通量。
Steady DC produces constant flux, so after the brief switch-on change there is no induced emf and no continuous transformer action.
稳定的直流电产生恒定的磁通量，因此在短暂的开关闭合变化之后，不会产生感应电动势，也不会有持续的变压器作用。
A field describes a force effect at positions in space.
场描述空间中各位置的力的作用效果。
Changing field strength, coil area, orientation or relative motion can change flux linkage.
改变场强、线圈面积、方向或相对运动均可改变磁链。
Watch for: A transformer needs changing magnetic flux; a steady DC input does not provide continuous transformer action.
请注意：变压器需要变化的磁通量；恒定的直流输入无法提供持续的变压作用。
An ideal transformer has 250 primary turns, 100 secondary turns, and a primary voltage of 20 V.
理想变压器有250个初级线圈匝数，100个次级线圈匝数，初级电压为20 V。
Find the secondary voltage.
求次级电压。
A steady DC input does not keep an ideal transformer working.
稳定的直流输入无法使理想变压器正常工作。
The result is a secondary voltage of 8 volts.
结果是次级电压为8伏。
The alternating current in the primary makes a changing magnetic flux in the iron core, which induces a voltage in the secondary.
初级线圈中的交流电在铁芯中产生变化的磁通量，从而在次级线圈中感应出电压。
With 200 turns to 50, the voltage falls by the same factor, 12 volts to 3.
匝数从200变为50，电压按相同比例下降，从12伏降到3伏。
An ideal transformer reduces 20 V to 5 V with primary current 0.30 A.
理想变压器将20 V降至5 V，初级电流为0.30 A。
Find secondary current and power.
求次级电流和功率。
Why does steady DC not fit the model?
为什么稳态直流电不符合该模型？
The power is 6 W, so the secondary current is 6 divided by 5, which is 1.2 A.
功率为 6 W，所以次级电流等于 6 除以 5，即 1.2 A。
Ideal power conservation exchanges voltage and current.
理想变压器中功率守恒，电压与电流此消彼长。
Induction requires changing flux, absent in the steady DC state.
电磁感应需要变化的磁通量，而稳恒直流状态下没有这种变化。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。