Induced Currents and Magnetic Forces · 感应电流与磁力
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| Lenz's law/ˈlentsɪz lɔː/ | 楞次定律 | léng cì dìng lǜ |
| eddy currents/ˈedi ˈkʌrənts/ | 涡电流 | wō diàn liú |
The induced current always fights the change that made it
- Push a magnet at a coil and the coil pushes back.
- The induced current flows the way that opposes the incoming change.
- This stubborn opposition is Lenz's law 楞次定律.
- It is the minus sign in Faraday's law, and it comes from energy conservation.
感应电流总是对抗产生它的那个变化
- 把磁体推向线圈,线圈就往回推。
- 感应电流朝着对抗到来的变化的方向流动。
- 这种固执的对抗就是楞次定律。
- 它是法拉第定律里的负号,来自能量守恒。
Lenz's law: oppose the change
- The induced current makes its own magnetic field.
- That field points so as to fight the change in flux.
- Push a north pole in, and the coil's near face becomes a north pole to repel it.
- Pull it out, and the coil turns south to try to hold it back.
楞次定律:对抗变化
- 感应电流产生它自己的磁场。
- 那个场的指向要对抗通量的变化。
- 把北极推进去,线圈近端的面就变成北极来排斥它。
- 把它拉出来,线圈就变成南极来试图留住它。
Watch the opposition · 观察对抗作用
Push the magnet in and out and see the induced current reverse to always oppose the change. · 将磁铁推入和拉出，观察感应电流反向以始终对抗这种变化。
The induced current in a coil always flows so that its magnetic field: · 线圈中的感应电流总是流动，使其磁场：
Lenz's law: the induced field always opposes the change. · 楞次定律：感应场总是对抗变化。
You push a north pole toward a coil. The coil's near face becomes a: · 你将北极推向线圈。线圈的近端面变成：
To oppose the approach, the near face turns north and repels. · 为了对抗接近，近端面变为北极并产生排斥力。
Why: you can't get free energy
- Suppose the induced current helped the magnet instead of opposing it.
- Then the magnet would speed up on its own, making even more current — free energy.
- That would break energy conservation, so nature forbids it.
- You must do work against the opposition to keep the flux changing.
为什么:你不能凭空得到能量
- 假设感应电流帮助磁体而不是对抗它。
- 那么磁体会自己加速,产生更多电流——凭空的能量。
- 那会打破能量守恒,所以自然界禁止它。
- 你必须对抗这种对抗做功,才能让通量持续变化。
Lenz's law is a direct consequence of the conservation of: · 楞次定律是守恒定律的直接结果：
If the current helped the change, you would get free energy — forbidden. · 如果电流帮助了变化，你将获得免费能量——这是被禁止的。
The opposition feels like a drag
- Because it opposes the motion, the induced current creates a resisting force.
- Move the magnet faster and the drag grows — you push harder, and more current flows.
- The mechanical work you do becomes the electrical energy induced.
- Opposition is exactly what makes induction an energy converter.
这种对抗感觉像阻力
- 因为它对抗运动,感应电流产生一个阻碍力。
- 把磁体移得更快,阻力就增大——你推得更用力,更多电流流动。
- 你做的机械功变成感应出的电能。
- 对抗正是让感应成为能量转换器的东西。
The induced current creates a force that opposes the motion causing it (a drag). · 感应电流产生的力对抗引起它的运动（阻力）。
The opposition acts as a drag; your work becomes electrical energy. · 对抗作用表现为阻力；你的功转化为电能。
Select all · 所有 true statements about Lenz's law. · 选择关于楞次定律的所有正确陈述。
Opposes the change, from energy conservation, acts as a drag. It never helps the change. · 对抗变化，源于能量守恒，表现为阻力。它从不帮助变化。
Everyday uses of the drag
- Eddy currents 涡电流 induced in a metal disc brake a train smoothly, with no pads.
- Induction cooktops heat a pan by driving eddy currents in its base.
- Metal detectors sense the eddy currents a coin induces.
- Each turns a changing flux into heat or a braking force.
阻力的日常用途
- 在金属圆盘中感应出的涡流平稳地为火车刹车,不用刹车片。
- 电磁炉通过在锅底驱动涡流来加热锅。
- 金属探测器感知一枚硬币感应出的涡流。
- 每一个都把变化的通量变成热或刹车力。
The swirling induced currents used for smooth braking are called ____ currents. · 用于平稳制动的涡旋感应电流被称为____电流。
Eddy currents brake trains and heat induction cooktops. · 涡流用于列车制动和加热感应灶台。
You push the north pole of a magnet toward a coil.
- By Lenz's law, the coil's near face becomes a north pole to repel it.
- You must do work pushing against that repulsion — that work becomes the induced electrical energy.
你把磁体的北极推向线圈。
- 由楞次定律,线圈近端的面变成北极来排斥它。
- 你必须对抗那个排斥做功——那份功变成感应出的电能。
The induced current always opposes the change, never helps it. If you ever find an induced current that reinforces the change, you have the direction backward — check with Lenz's law, which guarantees energy conservation.
感应电流总是对抗变化,从不帮助它。如果你发现某个感应电流增强了变化,那你的方向就搞反了——用楞次定律检查,它保证能量守恒。
Lenz's law: the induced current always opposes the change in flux — the minus sign in $\varepsilon = -d\Phi_B/dt$. It follows from energy conservation (no free energy), so the opposition feels like a drag; eddy currents use it for braking and induction heating.
楞次定律:感应电流总是对抗通量的变化——就是 $\varepsilon = -d\Phi_B/dt$ 里的负号。它源于能量守恒(没有凭空的能量),所以这种对抗感觉像阻力;涡流利用它来刹车和感应加热。