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

那领域什么时候改变？这就是诱发动势原因。

Yeah, but the EMF's no good. - Why?

没有 EMF不能用 - 怎么会？

Well, no traces of EMF, that's for sure.

没有动势反应 这点很确定。

I just swept the Telesca house with the EMF. It's clean.

我用EMF把特莱房子扫视过一遍 没什么发现。

So an emf is induced in the second coil.

因此在第圈中感应出一动势。

And emf, you’ll recall, stands for electromotive force, which is what causes electrons to move and form a current.

动势，你会记得，代表动势，这是导致子移动并形成流原因。

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

因此，通过第圈磁通量会 发生变化，从而产生动势。

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

这意味着通过圈中环路磁通量会随着时间而变化，这就是感应动势原因。

And as we'll soon see, the emf depends on the sine of the angle between the coil and the magnetic field.

我们很快就会看到，动势取决于圈和磁场之间夹角正弦值。

So we shorten this to say that the ideal voltage supplied by the battery is its emf.

所以我们缩小范围，说理想压 由池提供是它动势。

In maths terms, we’d say that the emf is equal to the negative of the change in flux, over the change in time.

在数学术语中，我们会说动势等于通量变化随时间变化负数。

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

它是负，因为感应动势 与主流方向相反。

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，我们将这想法称为法拉第感应定律：它说变化磁场会在圈中感应出动势。

This induction of an emf that opposes the main current is called self-inductance.

这种与主流相反动势感应 称为自感。

So, when you measure the actual voltage between the terminals of the battery, you get a value that's less than our ideal emf potential.

因此，当您测量池端子之间实际压时，您会得到低于我们理想动势位读数。

So, when you measure the actual voltage between the terminals of the battery, you get a value that’s less than our ideal emf potential.

因此，当您测量池端子之间实际压时， 您会得到一低于我们理想动势值。

Now, we can calculate the strength of the emf in a generator using some of the principles we talked about last time.

现在，我们可以使用我们上次讨论一些原理来计算生成器中动势强度。

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

这种关系也以相反方式起作用，变化磁通量会产生与磁通量相反动势。

And finally, instead of finding the emf in just one loop of wire, we're finding the emf in a whole coil of wire.

最后，我们不是在一圈中找到动势，而是在一整圈中找到动势。

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

当该领域发生变化时？ 这就是产生动势原因。