Prática de Shadowing: Current | Introduction to electrical engineering | Electrical engineering | Khan Academy - Aprenda a falar inglês com vídeo
Escolha um modo de prática
Cada modo abre uma sala de prática em tela cheia.
118 frases
Se as frases estiverem muito curtas ou longas, clique em Edit para ajustá-las.
1
All right, now we're going to talk about the idea of an electric current.
2
And the story about current starts with the idea of charge.
3
So we've learned that we have two kinds of charges, positive and negative charge.
4
We'll just make up two little charges like that.
5
And we know if they're the opposite sign, that there will be a force of attraction between them.
6
And if they have two like signs, here's two charges that are both positive.
7
And these charges are going to repel each other.
8
So this is the basic electrostatics idea.
9
And the same thing for two minus charges.
10
They also repel.
11
So like charges repel and unlike charges attract.
12
That's one idea.
13
So we have the idea of charge.
14
And now we need a place to get some charge.
15
And one of the places we'd like to get charge from is copper, copper wires.
16
A copper atom looks like this.
17
A copper atom has a nucleus with some protons in it.
18
And it also has electrons flying around the outside, electrons in orbits around the outside.
19
So we'll draw the electrons like this.
20
So there will be orbits around this nucleus.
21
Pretty good circles.
22
And there will be electrons in these little minus signs.
23
There's electrons stacked up in this.
24
And even farther out, there's electrons.
25
So there's a kind of an interesting -looking copper atom.
26
Copper, the symbol for copper is Cu, and its atomic number is 29.
27
29. That means there's 29 protons inside here, and there's 29 electrons outside.
28
And it turns out, just as a coincidence for copper, that the last orbital out here has just one electron in it.
29
That guy right there.
30
And that's the one that is the easiest to pull away from copper and have it go participate in conduction,
31
in electric current.
32
So if I have a chunk of copper,
33
every copper atom will have the opportunity to contribute this one lonely electron out here.
34
If we look at another element like, for instance, silver, silver has this same kind of electron configuration where there's just one out here.
35
And that's why silver and copper are such good conductors.
36
Alright, so now we're going to build, let's build a copper wire.
37
Here's sort of a copper wire.
38
It's just made of solid copper, it's all full of copper atoms.
39
And I'm going to put a voltage across this.
40
There's our little battery.
41
This is the minus sign, this is the plus sign.
42
and we'll hook up a battery to this.
43
And what's going on in here,
44
inside this copper, inside this copper is a whole bunch of electrons that are associated with atoms.
45
It's a neutral, it's a neutral piece of metal.
46
There's the same number of protons as there is electrons.
47
But these electrons are a little bit loose.
48
So if I put a plus over here, that's this situation right here where a plus is attracting a minus.
49
And so an electron is going to sort of wander over this way and go like that.
50
And that's going to leave sort of a net positive charge in this region.
51
And so these electrons are all going to start moving in this direction.
52
And down at the end, here, an electron is going to come out of this battery,
53
travel in here, and it's going to go in there and make up the difference.
54
So if I had a net positive charge here from the electrons leaving and going to the left, this battery would fill those in.
55
And I'm going to get a net movement of charge, of negative charge, around in this direction like this.
56
The question is, how do I measure that?
57
How do I measure or give a number to that amount of stuff that's going on?
58
So we want to quantify that.
59
We want to assign a number to the amount of current happening here.
60
So what we do is in our heads, we put a boundary across here.
61
So just make that up in your head.
62
And it cuts all the way through the copper.
63
And what we know, we're going to stand right here.
64
And we're going to keep our eye right on this boundary down in here.
65
And as we watch, what we're going to do is we're going to count the number of electrons that move by here.
66
And we're going to have a stopwatch, and we're going to time that.
67
And so we're going to get, basically, this is charge.
68
It's negative charge, and it's moving to the side.
69
And what we're going to do is at one little spot right here, we're just going to count the number that go by in one second.
70
And so we're going to get charge per second.
71
And it's going to be a negative charge moving by.
72
And that's what we call current.
73
and it's the same as water flowing by in a river that's the same idea
74
all right now I'm going to set up a different situation
75
that also get produces a current and this time we're going to do it with water water and salt
76
so here's here's just let's build a tube of salt of salt water like this so we're going to pretend
77
Again, this is some tube that's all full of water.
78
I'm also gonna put a battery here.
79
Let's put another battery.
80
And we'll stick the wire into there, and we'll stick the wire into there.
81
And this is the plus side of the battery, and this is the minus side of the battery.
82
So water is H2O, and this does not conduct.
83
There's no free electrons available here.
84
But what I'm gonna do is I'm gonna put some table salt in it.
85
This is ordinary salt that you put on your food, and it's made of sodium.
86
That's the symbol for sodium.
87
And chloride, Cl is chloride.
88
Sodium chloride is table salt.
89
If we sprinkle some table salt into water, what happens is these dissolve,
90
and we get a net plus charge here and a net minus charge on the chlorine.
91
So out here is floating around NAs with plus signs and CLs nearby, really close nearby, with minuses.
92
Let's keep it even, all right.
93
Now when I dip my battery wires into this water, what's going to happen is this plus charge,
94
this plus charge over here from the battery is going to attract the minus CLs.
95
So the CL is going to move that way a little bit.
96
And over here, the same thing is happening.
97
There's a minus sign here.
98
There's a minus from the battery.
99
And that's going to attract this, and it's also going to repel the Cl minuses.
100
And so what we get is a net motion of positive charge plus Q going this way,
101
and we get minus Q going this way.
102
And how do we measure that current?
103
How do we measure that current?
104
Well, we do it the same way as we did up there with copper.
105
We put a boundary through here in our heads.
106
We stand here, and we watch the charges moving by.
107
And what we're going to get is some sodiums, Na's, moving this way, and chlorines moving this way,
108
just like we showed here.
109
Na moving this way.
110
And so there's going to be plus charges moving through the boundary
111
and minus charges moving through the boundary in the opposite direction.
112
And if I take the total sum of that, for example, if I see one
113
Na go this way and one Cl go this way, that's equivalent to two charges moving through the boundary.
114
Hope that makes sense.
115
It's equivalent to two charges, one going this way and one going this way.
116
And because they have opposite signs, they add together and make two charges.
117
In this case, current is equal,
118
again, to charge per second.
Baixar aplicativo
Tudo o que você precisa para falar fluentemente
Pronúncia com IANota em cada frase
Prática de IPADomine cada som
VocabulárioMonte seu banco de palavras
Jogo de vocabulárioAprenda brincando
Mesmo canal
B11
Introduction to ratios | Ratios, rates, and percentages | 6th grade | Khan Academy
Daily ConversationHigh School Students
B16
LearnStorm Growth Mindset: How to write a SMART goal
American AccentBusiness EnglishHigh School StudentsUniversity Students
B19
States of matter | Middle school chemistry | Khan Academy
American AccentTOEFL PrepCambridge Exam PrepHigh School Students
B12
Newton's second law | Middle school physics | Khan Academy
American AccentHigh School StudentsUniversity Students
C15
Molecules, crystals, and diatomic elements | Middle school chemistry | Khan Academy
American AccentHigh School StudentsUniversity Students
B13
Atoms | Middle school chemistry | Khan Academy
American AccentTOEFL PrepCambridge Exam PrepHigh School Students
C13
Pixar in a Box | Welcome to Pixar in a Box | Khan Academy
American AccentHigh School StudentsUniversity Students
C14
Proportional reasoning with motion | AP Physics | Khan Academy
American AccentBusiness EnglishUniversity StudentsWorking Adults
C12
Biology overview
American AccentUniversity Students
C12
Newton, Leibniz, and Usain Bolt | Derivatives introduction | AP Calculus AB | Khan Academy
American AccentCambridge Exam PrepUniversity StudentsWorking Adults
B12
Elements | Middle school chemistry | Khan Academy
American AccentHigh School StudentsUniversity Students
C115
Introduction to high school physics | Khan Academy
American AccentHigh School StudentsUniversity Students
B12
Introduction to interest | Interest and debt | Finance & Capital Markets | Khan Academy
American AccentBusiness EnglishUniversity StudentsWorking Adults
C14
Derivative as slope of a tangent line | Taking derivatives | Differential Calculus | Khan Academy
American AccentCambridge Exam PrepUniversity StudentsWorking Adults
B2How to rationalize a denominator | Exponent expressions and equations | Algebra I | Khan Academy
Daily ConversationHigh School Students
FOR YOU
Vídeo recomendado
B21
183 frases
Concept of Electric Current with Train example | TheElectricalGuy
Daily ConversationUniversity Students
C11
29 frases
What are Ionic Bonds? | Properties of Matter | Chemistry | FuseSchool
Daily ConversationUniversity Students
C11
7 frases
Diodes Explained - The basics how diodes work working principle pn junction
Daily ConversationUniversity StudentsWorking Adults
![[Lecture Ready3] Ch10 Lecture2](https://img.youtube.com/vi/8FVVfebHarQ/mqdefault.jpg)
C11
111 frases
[Lecture Ready3] Ch10 Lecture2
Daily ConversationUniversity Students
C1552 frases
The Professor Who Taught People How To Think (1962)
Daily ConversationUniversity StudentsWorking Adults
C13
279 frases
LET THERE BE... Voltage? | Maxwell's Equation #2 Explained for Beginners
Daily ConversationUniversity Students
C11
86 frases
The Composition and Function of Blood
Daily ConversationUniversity Students
C11
40 frases
The Engineering that Runs the Digital World 🛠️⚙️💻 How do CPUs Work?
Daily ConversationUniversity StudentsWorking Adults
C12
28 frases
What is IMC (Intermetallic Compounds) part II? The different between IMC, alloy, eutectic
Daily ConversationUniversity StudentsWorking Adults
C11
176 frases
Every Networking Concept Explained | Networking 101 (2026)
Daily ConversationUniversity StudentsWorking Adults
C11
19 frases
I Made an EMP Device... It Actually Works
Daily ConversationUniversity StudentsWorking Adults
C13
298 frases
GENERAL CHEMISTRY explained in 19 Minutes
Daily ConversationUniversity Students
Vocabulário e dicas de fala para esta lição
As palavras que mais se repetem: charge, copper, electron, minus, battery. Este vídeo tem 118 frases e 1319 palavras para praticar shadowing. A fala dura 9:15. O falante mantém um ritmo estável de cerca de 143 palavras por minuto, confortável para o shadowing. 85% das palavras estão entre as 3.000 mais comuns do inglês; vale a pena estudar o restante antes de começar.
Vocabulário principal deste vídeo
15 palavras do vídeo que vale a pena aprender, com pronúncia e significado:
| Palavra | Pronúncia | Significado |
|---|---|---|
| copper substantivo | /ˈkɒpə/ | cobre |
| minus | /ˈmaɪ.nəs/ | menos |
| wire substantivo | /ˈwaɪɚ/ | arame |
| boundary substantivo | /ˈbaʊndɹi/ | fronteira |
| atom substantivo | /ˈætəm/ | átomo |
| electron substantivo | /ɪˈlɛk.tɹɑn/ | elétron, eletrão |
| attract verbo | /əˈtɹækt/ | atrair |
| sodium substantivo | /ˈsəʊ.di.əm/ | sódio |
| tube substantivo | /tuːb/ | tubo, bisnaga |
| symbol substantivo | /ˈsɪmbəl/ | símbolo |
| neutral adjetivo | /ˈnuː.tɹəl/ | neutro |
| orbit substantivo | /ˈɔɹ.bɪt/ | órbita, círculo |
| nucleus substantivo | /ˈnuː.kli.əs/ | núcleo |
| element substantivo | /ˈɛləmənt/ | fundamento |
| ordinary adjetivo | /ˈɔɹdɪnɛɹi/ | ordinário, normal |
Phrasal verbs que você vai ouvir
| Palavra | Pronúncia | Significado |
|---|---|---|
| make up verbo | /ˌmeɪk ˈʌp/ | compensar |
| hook up verbo | conectar | |
| set up verbo | /ˌsɛt ˈʌp/ | preparar |
| turn out verbo | terminar |
Frases que vale a pena repetir
Frases curtas e completas do vídeo que você pode usar na conversa do dia a dia:
- We'll just make up two little charges like that.
- The question is, how do I measure that?
- I'm also gonna put a battery here.
- Let's keep it even, all right.
- How do we measure that current?
Pronúncia para ficar de olho
O falante usa 32 contrações e formas reduzidas, como we're, I'm, we'll. Diga-as na forma curta, do jeito que você ouve.
- Os sons de “sh” e “zh”: associate /əˈsoʊʃi.ət/, attraction /əˈtɹækʃn̩/, configuration /kənˌfɪɡ.əˈɹeɪ̯.ʃən/, conduction /kənˈdʌkʃən/
- Palavras longas — acerte a sílaba tônica: ordinary /ˈɔɹdɪnɛɹi/, participate /pɑːˈtɪs.ɪ.peɪt/, associate /əˈsoʊʃi.ət/, configuration /kənˌfɪɡ.əˈɹeɪ̯.ʃən/, coincidence /kəʊˈɪnsɪdəns/
Sons difíceis para falantes de português:
- Consoante final — sem acrescentar um “i” depois: attract /əˈtɹækt/, tube /tuːb/, orbit /ˈɔɹ.bɪt/, element /ˈɛləmənt/, participate /pɑːˈtɪs.ɪ.peɪt/
- /l/ final — a língua toca o céu da boca, não vira “u”: symbol /ˈsɪmbəl/, neutral /ˈnuː.tɹəl/, repel /ɹɪˈpɛl/, sprinkle /ˈspɹɪŋkəl/
- s + consoante no início — sem um “i” antes: stack /stæk/, sprinkle /ˈspɹɪŋkəl/
Como praticar com este vídeo
- Ouça o vídeo inteiro uma vez sem falar e anote as palavras que você não conhece.
- Faça shadowing frase por frase na velocidade normal, repetindo cada uma até o seu ritmo ficar igual ao do falante.
- Grave a sua voz e compare com o original, prestando atenção a palavras como copper, minus, wire.
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.