And when that field changes? That’s what induces an emf.

那个领域什么时候改变？这就是诱发电动势的原因。

So the magnetic flux through the second coil changes, which induces an emf.

因此，通过第二个线圈的磁通量会 发生变化，从而产生电动势。

And it's negative, because the induced emf is in the opposite direction of the main current.

它是负的，因为感应电动势 与主电流方向相反。

And when that field changes? That's what induces an emf.

当该领域发生变化时？ 这就是产生电动势的原因。

And to calculate an induced emf, you just take the change in current over time and multiply it by negative L.

要计算感应电动势，只需将电流随时间的变化乘以负。

This means that the magnetic flux through the loops in the coil changes over time, which is what induces an emf.

这意味着通过线圈中的环路的磁通量会随着时间而变化，这就是感应电动势的原因。

It says that a changing magnetic field will induce an emf in a loop of wire.

它说不断变化的磁场会 在线圈中感应出电动势。

But a couple of other things induced emf, too, even if the strength of the magnetic field stayed the same.

但是，即使磁场强度保持不变，其他一些因素也会引起电动势。

And this relationship works the opposite way as well, with a changing magnetic flux inducing an emf that opposes the flux.

这种关系也以相反的方式起作用，变化的磁通量会产生与磁通量相反的电动势。

So now Faraday knew that when a magnetic field changed over time, it induced an emf in a loop of wire.

所以现在法拉第知道，当磁场随时间变化时，它会在线圈中感应出一个电动势。

The magnetic flux through the loop changes, which induces an emf.

通过环路的磁通量发生变化， 从而产生电动势。

The AC power running through the charging pad induces an emf in your phone's coil, which can use the energy to charge its battery.

流经充电板的交流电源会在手机线圈中感应出电动势，从而可以使用该能量为电池充电。

But when it comes to inducing emf, what really matters is how the flux is changing over time.

但是当涉及到感应电动势时，真正 重要的是通量如何随时间变化。

These days, we call this idea Faraday’s Law of Induction: It says that a changing magnetic field will induce an emf in a loop of wire.

如今，我们将这个想法称为法拉第感应定律：它说变化的磁场会在线圈中感应出电动势。

So the strength of the induced emf will be equal to all of that, divided by the change in time.

所以感应电动势的强度将 等于所有这些，除以时间的变化。

Today, you learned about magnetic flux, and how a change in magnetic flux can induce an emf in a loop or coil of wire.

今天，您了解了磁通量，以及磁通量的变化如何在线圈或线圈中产生电动势。

And the key here is that a change in the magnetic flux through a coil induces the same emf in each loop of the coil.

这里的关键是，通过线圈的磁通量变化会在线圈的每个回路中感应出相同的电动势。

So in an AC circuit, what you end up with is a changing current that induces an opposing magnetic flux, which in turn induces an emf in the opposite direction of the current!

所以在交流电路中，你最终得到的是一个变化的电流，它会感应出一个相反的磁通量，这反过来又会在电流的相反方向上感应出一个电动势！

But often, you’ll be inducing emf in a coil of wire – like what Faraday was doing in his experiment – so it helps to know how a change in the magnetic flux will induce emf in a coil.

但通常情况下，你会在线圈中感应出电动势——就像法拉第在他的实验中所做的那样——所以了解磁通量的变化如何在线圈中感应出电动势是有帮助的。

Which means that the induced emf in a coil of wire is equal to the number of coils, times the change in magnetic flux over the change in time, all multiplied by a negative sign.

这意味着线圈中的感应电动势为 等于线圈数乘以磁通量随时间变化的变化，全部乘以负号。