好吧。让我们谈谈波速。特别是它与频率和波长的关系。这真的是在介绍物理学中的这种类型的问题中看到的最重要的事情。
好吧。现在，波浪的运动是由于波浪的东西只是由干扰产生的东西，然后只是通过介质传播自己的温度，波的运动仅取决于介质本身的性质。这意味着它的速度只能取决于介质。但这并不意味着它与波长和周期无关。它确实取决于波长和周期。只是通过标准公式。速度等于距离的距离。现在，如果我有一个经过媒体传播的定期波，它会走多远？好吧，如果我在谈论一个干扰之一，那么距离等于波长。多久时间？ Well, if I'm talking about one of the disturbances, the time is equal to the period. And that means that speed equals wavelength divided by period.
现在，我们可以以通过取得这种因子的形式在更常见的形式中写入这一点，并记住在该期间的一个等于频率。这样，意味着速度等于波长倍率频率。这个等式非常常见。你会在这个单位的物理中看到它。好吧。让我们看看这意味着什么。
如果我在谈论通过相同媒体传播的波，那么速度必须是恒定的。这意味着频率恒定的波长倍。这样，这意味着如果波长上升，频率必须下降。反过来。如果波长下降，则频率将上升。因此，长波长波具有非常非常小的频率，而短波长波，也非常快，它们有高频。好吧。让我们看看我们如何使用这个想法来解决一些问题。
程序相当简单，但我想说明一些人的常见错误。好吧。所以第一向前向前，波的波长为2厘米，频率为300赫兹。它的速度是多少？嗯，v等于lambda f。所以我要说，好吧，v等于lambda f。所以Lambda是2厘米，F是300赫兹。所以当我乘以2到300时，我得到600但是现在单位是什么？好吧，好吧，如果我直接这样做，那将是厘米。赫兹每秒波浪。 So this will be per second. But of course that's not SI. What I really should do is I should absorb this 100 into the sente and write the answer as 6 meters per second. And if I do that, no problem at all. And if I don't remember to do that and it's a free response problem, I'm fine. So long as I wrote it as centimeters per second, it's not wrong. Totally right. But if it's a multiple choice problem, chances are the answer's going to be given like that and I got to be able to recognize that.
好吧。问题2.波通过波长为20个小米米的介质传播。所以现在我想知道频率两倍的波浪的波长是什么。好吧。现在。我不知道速度在这里。所以我真的不能，我无法获得频率。所以但是我不需要。因为我知道波长倍率是恒定的。所以我将频率乘以2.所以这对波长有什么意义？ Well, if the product's constant and I got a 2 here, I got to have a half here. So I'm going to multiply the wavelength by a half and a half of 20, 10. So there it goes. Alright? Now the idea is I didn't have to have numbers for everything. Often problems are given in that way in units like this, and so you just have to know how to set it up. It's not difficult but you just have to know how to do it and it just takes some practice. Alright.
所以让我们看看最后一个。具有21个模米波长的波浪进入介质，其中波速第三。好吧。现在，这里有什么东西。我们不再是在同一个媒介中。好吧。现在，当我们进入不同的媒体时，我们必须记住一些事情。频率既不能改变也不会改变。所有其他投注都关闭，频率和时期必须保持不变。只要它是相同的波，频率和时段都是相同的。 Everything else can change, alright?
因此，进入一个第三波速度的媒体，我想知道新的波长。好吧。这是想法。速度等于波长倍率频率。我们说频率不能改变，速度下降了一个倍数3.频率是相同的。无法改变。那么对波长有什么意义？这意味着波长必须达到三倍，因为允许波长改变。所以，一旦我们认识到，问题变得容易。21除以3是7.我们已经完成了。 But we need to understand that simple fact. Now I've seen a lot of problems that are written even easier than this where it will say, what's the new frequency? It will give us frequencies instead or does the frequency go up, go down or remain the same? The frequency got to remain the same, because frequency can't change. And as son as we recognize that and that this equation is always true, wavelength and speed got to do the same thing.
好吧。那是波速。
