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关于电能的重大误解

The Big Misconception About Electricity

This video was sponsored by Caséta by Lutron.
这个视频由路创卡塞塔赞助播出
Imagine you have a giant circuit
想象你有一个巨大的电路
consisting of a battery, a switch, a light bulb,
由一块电池 一个开关 一个灯泡
and two wires which are each 300,000 kilometers long.
和两根30万公里长的电线组成
That is the distance light travels in one second.
也就是光在一秒内传播的距离
So, they would reach out half way to the moon
所以它们会到达地月距离的一半
and then come back to be connected to the light bulb,
然后再返回接通灯泡
which is one meter away.
就在1米远的地方
Now, the question is,
现在有个问题
after I close this switch,
在我关闭开关后
how long would it take for the bulb to light up.
灯泡多久会亮
Is it half a second,
半秒
one second,
1秒
two seconds,
2秒
1/c seconds,
1/c秒
or none of the above.
或者都不是
You have to make some simplifying assumptions
你需要为这个电路做一些
about this circuit,
简化假设
like the wires have to have no resistance,
比如导线必须没有电阻
otherwise this wouldn’t work
否则无法工作
and the light bulb has to turn on immediately
还有当电流穿过的时候
when current passes through it.
电灯泡必须立即打开
But I want you to commit to an answer
但我希望你能给出一个答案
and put it down in the comments
然后在留言区评论
so you can’t say,
这样你就不会
oh yeah I knew that was the answer,
在我告诉你答案的时候说
when I tell you the answer later on.
我就知道是这样
This question actually relates to how electrical energy
这个问题实际上是关于电力
get from a power plant to your home.
是如何从发电厂到你家的
Unlike a battery,
和电池不同
the electricity in the grid
电网中的电
comes in the form of alternating current, or AC,
以交流电的形式存在
which means electrons in the power lines
也就是说输电线中的电子
are just wiggling back and forth.
只是在来回摆动
They never actually go anywhere.
而不会去任何地方
So, if the charges don’t come from the power plant
那么 如果电荷不会从发电站
to your home,
传到你家
how does the electrical energy actually reach you?
电能又是怎样到你家的呢?
When I used to teach this subject,
我以前教这门课的时候
I would say that power lines
我会说电线
are like this flexible plastic tubing
就像这个柔软的塑料管
and the electrons inside are like this chain.
里面的电子就像这根链条
So, what a power station does,
发电站所做的
is it pushes and pulls the electrons back and forth
就是来回推拉电子
60 times a second.
每秒60次
Now, at your house,
现在 你可以在家里
you can plug in a device, like a toaster,
接入一个设备 比如烤面包机
which essentially means
也就是说
allowing the electrons to run through it.
允许电子穿过它
So when the power station pushes and pulls the electrons,
当发电站推拉电子的时候
well, they encounter resistance in the toaster element,
它们在烤面包机元件中遇到阻力
and they dissipate their energy as heat,
然后以热能的形式释放能量
and so you can toast your bread.
这样你就可以烤面包了
Now, this is a great story,
这是个很好的演示
I think it’s easy to visualize,
很容易想象
and I think my students understood it.
我想我的学生能够明白
The only problem is, it’s wrong.
唯一的问题在于 这是错的
For one thing,
首先
there is no continuous conducting wire
没有连续不断的导线
that runs all the way from a power station to your house.
从发电站一直延伸到你家
No, there are physical gaps,
因为会有物理间隙
there are breaks in the line,
导线之间有缝隙
like in transformers
像在变压器中
where one coil of wire is wrapped on one side,
一个线圈缠绕在一边
a different coil of wire is wrapped on the other side.
另一个的线圈缠绕在另一边
So, electrons cannot possibly flow
电子不可能
from one the other.
在它们之间流动
Plus, if it’s the electrons
另外 如果电子
that are carrying the energy
把能量从发电站
from the power station to your device,
输送到你的设备
then when those same electrons
那么当这些相同的电子
flow back to the power station,
回流到发电站的时候
why are they not also carrying energy
为什么不把能量
back from your house to the power station?
从你家带回去呢
If the flow of current is two ways,
如果电流是双向的
then why does energy only flow in one direction?
为什么能量只往一个方向流动
These are the lies you were taught about electricity,
这些就是你被灌输的关于电的悖论
that electrons themselves have potential energy,
电子本身有势能
that they are pushed or pulled
它们被推拉
through a continuous conducting loop
穿过一个连续的传导环路
and that they dissipate their energy in the device.
然后在设备中释放能量
My claim in this video
我认为
is that all of that is false.
这些都是错误的
So, how does it actually work?
那么 它究竟是怎么工作的
In the 1860’s and 70’s,
在1860和70年代
there was a huge breakthrough
我们对宇宙的认知
in our understanding of the universe
有了巨大的突破
when Scottish physicist, James Clerk Maxwell,
当时的苏格兰物理学家麦克斯韦
realized that light is made up
意识到光是由
of oscillating electric and magnetic fields.
振荡的电场和磁场组成的
The fields are oscillating perpendicular to each other
电场相互垂直振荡
and they are in phase,
它们是同相的
meaning when one is at its maximum,
当一个震荡达到最大值时
so is the other wave.
另一个也会达到最大值
Now, he works out the equations
他计算出了
that govern the behavior of electric and magnetic fields
控制电场和磁场行为的方程
and hence, these waves,
因此 这些波
those are now called Maxwell’s equations.
那被称为麦克斯韦方程
But in 1883,
但在1883年
one of Maxwell’s former students, John Henry Poynting,
麦克斯韦以前的一名学生 坡印庭
is thinking about conversation of energy.
在思考能量的交流
If energy is conserved locally in every tiny bit of space,
如果能量在任何微小空间都是守恒的
well, then you should be able to trace the path
那么你就能追踪能量
that energy flows from one place to another.
流动的路径
So, think about the energy that comes to us from the sun,
因此 想想从太阳传到我们的能量
during those eight minutes when the light is traveling,
在光线传播的八分钟内
the energy is stored and being transmitted
能量在光的电场和磁场中
in the electric and magnetic fields of the light.
被储存并传递
Now, Poynting works out an equation
坡印庭列出了一个方程
to describe energy flux,
来描述能量流
that is, how much electromagnetic energy
也就是单位面积内
is passing through an area per second.
每秒有多少电磁能量流过
This is known as the Poynting vector
它被称为坡印亭矢量
and it’s given the symbol S.
用S来表示
And the formula is really pretty simple,
这个方程式十分简单
it’s just a constant one over mu naught,
只包含μ₀分之一
which is the permeability of free space
也就是真空磁导率
times E X B.
乘以E乘以B
Now, E X B,
E乘以B
is the cross product
是电场和磁场的
of the electric and magnetic fields.
向量积
Now, the cross product is just a particular way
向量积是将两个向量相乘的
of multiplying two vectors together,
一种特殊方式
where you multiply their perpendicular magnitudes
当你乘以它们的垂直幅度
and to find the direction,
并寻找方向时
you put your fingers in the direction of the first vector,
把你的四指指向第一个向量的方向
which in this case is the electric field,
这里指的是电场的方向
and curl them in the direction of the second vector,
并把它们向第二个向量的方向弯曲
the magnetic fields,
也就是磁场的方向
then your thumb points
那么你的大拇指指向的
in the direction of the resulting vector,
就是所求矢量的方向
the energy flux.
即能量流向
So, what this shows us about light
由此可知 光的能量
is that the energy is flowing perpendicular
是垂直流向
to both the electronic an the magnetic fields.
电场和磁场的
And it’s in the same direction as the light is traveling,
这也是光的传播方向
so this makes a lot of sense.
这很有道理
Light carries energy from its source
光将能量从源头
out to its destination.
输送到目的地
But the kicker is this,
但重点在于
Poynting’s equation doesn’t just work for light,
坡印廷等式并不仅适用于光线
it works anytime there are electric
只要电场和磁场同时存在
and magnetic fields coinciding.
该公式就适用
Anytime you have electric and magnetic fields together,
只要同时存在电场和磁场
there is a flow of energy
就有能量流动
and you can calculate using Poynting’s vector.
就可以使用坡印廷矢量来计算
To illustrate this,
为了解释这一点
let’s consider a simple circuit
假设一个有电池
with a battery and a light bulb.
和灯泡的简单电路
The battery by itself has an electric field
电池自身有电场
but since no charges are moving,
但目前没有电荷流动
there is no magnetic field
没有磁场
so the battery doesn’t lose energy.
因此这个电池没有流失能量
When the battery is connected into the circuit,
当这个电池接入电路时
its electric field extends through the circuit
它的电场以光速
at the speed of light.
进入电路
This electric field pushes electrons around
这个电场推动电子运动
so they accumulate on some of the surfaces of the conductors
因此 它们积聚在导体的某些表面上
making them negatively charged,
使导体磁场改变
and are depleted elsewhere
并在其他地方耗尽
leaving their surfaces positively charged.
在导体表面留下正电荷
These surface charges
这些表面电荷
create a small electric field inside the wires,
在导体内部产生了一个微小的电场
causing electrons to drift
使电子
preferentially in one direction.
优先向同一方向移动
Note that this drift velocity is extremely slow
这种移动速度非常慢
around a tenth of a millimeter per second.
大约是每秒十分之一毫米
But this is current,
但这种电流
well, conventional current
常规电流
is defined to flow opposite the motion of electrons,
被认为与电子移动方向相反
but this is what’s making it happen.
但这就是它产生的原因
The charge on the surfaces of the conductors
导体表面的电荷
also creates an eclectic field outside the wires
同样在电线外产生了一个电场
and the current inside the wires
导线内部的电流
creates a magnetic field outside the wires.
在导线外部产生一个磁场
So, now there is a combination
电场和磁场
of electric and magnetic fields
在电路周围
in this space around the circuit.
结合
So, according to Poynting’s theory,
依据坡印廷理论
energy should be flowing
能量应该流动
and we can work out the direction of this energy flow
我们可以使用右手法则
using the right hand rule.
找出能量流动的方向
Around the battery for example,
例如 在电池周围
the electric field is down
电场向下
and the magnetic field is into the screen.
磁场方向朝向屏幕里
So, you find the energy flux is to the right
因此 能量向右流动
away from the battery.
即远离电池的方向
In fact, all around the battery,
事实上 在电池周围
you’ll find the energy is radially outwards.
能量向外呈放射状
Energy is going out through the sides of the battery
能量从电池内部流到
into the fields.
电磁场中
Along the wires, again,
沿着导线 同样的
you can use the right hand rule
可以使用右手法则
to find the energy is flowing to the right.
发现能量向右流动
This is true for the fields along the top wire
这在上半部分导线
and the bottom wire.
和下半部分导线中都成立
But at the filament,
但在灯丝中
the Poynting vector is directed in toward the light bulb.
坡印廷矢量朝向灯泡里
So, the light bulb is getting energy from the field.
因此 灯泡从场中得到能量
If you do the cross product,
如果做向量积
you find the energy is coming in from all around the bulb.
你会发现能量从周围进入电灯
It takes many paths from the battery to the bulb,
从电池到灯泡有许多路径
but in all cases,
但在所有情况下
the energy is transmitted
能量都通过
by the electric and magnetic fields.
电场和磁场传输
– People seem to think that you’re pumping electrons
-人们可能认为你在抽取电子
and that you’re buying electrons or something,
你在买电子或其他的东西
which is just so wrong. (laughs)
但这是错的 [笑]
For most people,
时至今日
and I think to this day, it’s quite counterintuitive
对大多数人和我来说
to think that the energy is flowing through the space
想象能量流经导体周围的空间
around the conductor,
是十分违背直觉的
but the energy is,
但能量确实
which is traveling through the field,
迅速地在场中
yeah, is going quite fast.
传播
– So, there are a few things to notice here.
-因此 需要注意的是
Even though the electrons go two ways
虽然电子有远离和趋向电池
away from the battery and towards it,
两种移动方式
by using the Poynting vector,
但通过使用坡印廷矢量
you find that the energy flux only goes one way
你会发现能量只有一种流动方式
from the battery to the bulb.
即从电池到灯泡
This also shows it’s the fields
这也可以证明
and not the electrons that carry the energy.
是场而不是电子携带能量
– How far do the electrons go
电子在你正在谈论的这个小东西中
in this little thing you’re talking about,
走了多远
they barely move,
它们很少
they probably don’t move at all.
甚至根本不移动
– Now, what happens if in place of a battery,
-那么 如果我们在电池里
we use an alternating current source?
使用交流电会发生什么呢
Well then, the direction of current
电流的方向
reverses every half cycle.
每半圈反转一次
But this means that both the electric and magnetic fields
但这意味着电场和磁场
flip at the same time,
同时反转
so at any instant,
因此 无论何时
the Poynting vector still points in the same direction,
坡印廷矢量总是指向同一方向
from the source to the bulb.
从源头到灯泡
So the exact same analysis we used for DC
因此 我们对直流电的分析完全适用于
still works for AC.
交流电
And this explains how energy is able to flow
这也解释了能量为什么能
from power plants to home in power lines.
通过电源线从供电站流向你家
Inside the wires,
在电线中
electrons just oscillate back and forth.
电子仅在来回摆动
Their motion is greatly exaggerated here.
它们的移动在这被大大夸张了
But they do not carry the energy.
但它们并不携带能量
Outside the wires,
在电线外
oscillating eclectic and magnetic fields
摆动的电场和磁场
travel from the power station to your home.
从供电站传输到你家
You can use the Poynting vector to check
你可以使用坡印廷矢量
that the energy flux is going in one direction.
来验证能量仅沿一个方向流动
You might think this is just an academic discussion
你也许认为这只是一个学术猜想
that you couldn’t see the energy as transmitted
你不能看到能量通过场
either by fields or by the current in the wire.
或者电线内部的电流传输
But that is not the case,
但事实并非如此
and people learned this the hard way
人们开始铺设海底电缆时
when they started laying undersea telegraph cables.
以艰难的方式学到了这一点
The first Trans Atlantic cable was laid in 1858.
1858年铺设了第一条跨大西洋电缆
– It only worked for about a month,
-它只工作了大约一个月
it never worked properly.
且并非正常工作
– There are all kinds of distortions
-当人们试图发射信号时
when they try to send signals.
出现了各种失真
– Enormous amounts of distortion.
-巨大数量的失真
They could work it at a few words per minute.
他们可以以每分钟几个字的速度工作
– What they found was sending signals
-他们发现 传输的信号
over such a long distance under the sea,
在海底通过如此长距离后
the pulses became distorted and lengthened.
脉冲被扭曲 拉长
It was hard to differentiate dots from dashes.
很难区分点和破折号
To account for the failure,
为了找到错误原因
there was a debate among scientists.
科学家们之间有一场辩论
William Thomson, the future Lord Kelvin,
威廉汤姆森 未来的凯文勋爵
thought electrical signals moved through submarine cables
认为电信号通过海下电缆
like water flowing through a rubber tube.
就像水通过橡胶水管一样
But others like Heaviside and Fitzgerald,
但其他人 例如海维赛德和菲茨杰拉德
argued it was the fields around the wires
认为在电线周围存在场
that carried the energy and information.
场携带能量和信息
And ultimately,
最终
this view proved correct.
这种观点被证实
To insulate and protect the submarine cable,
为了绝缘和保护海底电缆
the central copper conductor
中心铜导体
had been coated in an insulator
涂覆在绝缘体中
and then encased in an iron sheath.
然后涂覆在铁护套中
The iron was only meant to strengthen the cable,
铁只是为了加固电缆
but as a good conductor,
但作为一种良好导体
it interfered with a propagation of electromagnetic fields
它干扰了电磁场的传播
because it increased the capacitance of the line.
因为它增大了导线的电容
This is why today, most power lines are suspended high up.
这也是现今大部分输电线高悬的原因
Even the damp earth acts as a conductor,
潮湿的土地也可以成为导体
so you want a large insulating gap of air
因此需要大量空气绝缘间隙
to separate the wires from the ground.
来将电线与地面隔开
So, what is the answer
我们巨型电路灯泡
to our giant circuit light bulb question?
问题的答案是什么呢
Well, after I close the switch,
我闭合开关以后
the light bulb will turn on almost instantaneously,
灯泡基本上会立刻亮起
in roughly 1/C seconds.
大约仅需1/C秒
So, the correct answer is D.
所以正确答案是D
I think a lot of people imagine
我猜许多人会认为
that the electric field needs to travel
电场需要从电池
from the battery,
一直沿导线
all the way down the wire
传输
which is a light second long,
需要一光秒
so it should take a second for the bulb to light up.
所以灯泡亮起需要一秒
But what we’ve learned in this video
我们从这个视频中学到的
is it’s not really what’s happening in the wires
重点不是电线里真的发生了什么
that matters,
而是
it’s what happens around the wires.
电线周围发生了什么
And the electric and magnetic fields
电场和磁场
can propagate out through space
在空间中传播
to this light bulb,
到这个一米远的灯泡
which is only one meter away in a few nanoseconds.
仅需几纳秒
And so, that is the limiting factor
这是灯泡亮起
for the light bulb turning on.
的限制因素
Now, the bulb won’t receive
这个灯泡无法
the entire voltage of the battery immediately,
立即接收电池的全部电压
it’ll be some fraction,
一部分是因为
which depends on the impedance of these lines
导线和灯泡
and the impedance of the bulb.
的电阻
Now, I asked several experts about this question,
就此问题 我咨询了一些专家
and got kind of different answers,
得到了一些不同的答案
but we all agreed on these main points.
但我们都认同这个主要原因
So, I’m gonna put their analysis in the description
如果你想了解的更多信息相关信息
in case you want to learn more about this particular setup.
我在简介下描述了他们的分析
If I get called out on it
如果我说出来
and people don’t think it’s real,
人们不会相信
we can definitely invest the resources
我们绝对可以投入资源
and string up some lines,
串起一些线路
and make our own power lines in the desert.
在沙漠中制作我们自己的电线
– I think you’re gonna get called out on it.
-我认为你需要说出来
– I agree, I think you’re gonna get called out.
-我同意 我想你需要说出来
(laughing)
[笑]
I think that’s right.
-我觉得对
– I think it’s just kinda wild
-我觉得有点奇怪
that this is one of those things
那些我们每天
that we use everyday,
都在使用的东西
that almost nobody thinks about
却几乎没人思考
or knows the right answer to.
或者知道正确答案
These traveling electromagnetic waves around power lines
这些在电线周围传播的电磁场波
are really what’s delivering your power.
才真正地传输能量
Hey, now that you understand
嘿 你现在明白
how electrical energy actually flows,
电能怎样流动了
you can think about that
每次你打开照明开关时
every time you flick on a light switch.
你都可以想一想
And if you want to take your switches to the next level,
如果你想将升级你的开关
the sponsor of this video, Caseta by Lutron,
这个视频的赞助商 路创卡塞塔
provides premium smart lighting control,
提供优质的智能照明控制
including switches, remotes, and plug-in smart dimmers.
包括开关 遥控器和插入式智能调光器
And since one switch can control many regular bulbs,
由于一个开关可以控制许多常规灯泡
you can effectively make all those bulbs smart
你可以仅通过更换开关
just by replacing the switch.
有效地使所有灯泡变得智能
Then, you can turn your lights on and off
然后 你可以用你的手机
using your phone,
控制灯泡开关
or you can use another device
其他装置也可以
like Alexa or Google Assistant.
比如亚莉克莎或谷歌助手
Caseta works with more leading smart home brands
与其他智能灯泡控制系统相比
than any other smart lighting control system.
卡塞塔合作的领先的智能家居品牌更多
One of the things I like is setting timers.
我喜欢的一个功能是设置时间
The lights in my office for example,
例如在我办公室的灯泡
turn on by themselves every evening.
每晚会自动亮起
And this feature gives you peace of mind
此功能可让你放心
that everyone in your household
每个人回到家时
will always come home to a well-lit house.
家里光线都是充足的
And once you’re already in bed,
躺在床上之后
you can check which lights you forgot to turn off
你可以用手机检查哪个灯忘关了
and do that from your phone.
并用手机关掉
Installation is easy.
安装十分简单
Make sure you turn off power to the switch first
首先确保关闭交换机的电源
and then disconnect the existing wires
然后断开现有电线的连接
and connect Caseda’s smart switch.
再将卡塞塔的智能开关装上
If you need any help,
如果你需要帮助
they’re just a click or a call away.
仅需点击或者电话就可以联系他们
Learn more about Caseda at Lutron’s website,
在路创网站能了解更多卡塞塔的信息
lutron.com/veritasium.
lutron.com/veritasium.
I will put that link down in the description.
我会在简介里放上链接
So, I want to thank Lutron Electronics
在此感谢路创电器
for sponsoring this video,
赞助本视频
and I want to thank you for watching.
谢谢观看

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视频概述

电能是怎样从发电站到你家的?打开开关灯泡需要多久才能亮起?

听录译者

收集自网络

翻译译者

nis

审核员

审核员ZZ

视频来源

https://www.youtube.com/watch?v=bHIhgxav9LY

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