シャドーイング練習: Ohms Law Explained - The basics circuit theory - 動画で英語スピーキングを学ぶ

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Hey there guys, Paul here from theengineeringmindset .com.

In this video we're going to be looking at Ohm's Law

to understand how it works as well as how to use it.

There are also two problems at the end of this video for you to test your knowledge

and see if you can solve.

So what is Ohm's Law?

Ohm's Law is the relationship between voltage, current and resistance and how they relate to each other.

Ohm's law was developed by a German physicist named George Ohm

who undertook many experiments to develop his theory including measuring current by touching live electrical circuits to see how much it hurt.

As you might imagine the higher the current the more it hurt.

Now there are three formulas we need to use for Ohm's law

but we don't actually need to remember these and I'll show you a super easy tip in just a moment.

So the three formulas we use for Ohm's law are voltage equals current multiplied by resistance, current equals voltage divided by resistance,

and resistance equals voltage divided by current.

If that seems like a lot to remember then don't worry because we don't need to remember them.

All we need to remember is Ohm's triangle which looks like this.

So you just need to remember these three letters in order V, I, R.

Then we just write those letters in a triangle with V at the top

and we draw a line to separate the letters.

In fact you don't even need to remember those

because I've made a free PDF guide for you with some worked examples

which you can keep on your PC or your mobile and access wherever you need.

Links for that can be found in the video description down below.

Now all we do when we need to use a formula is cover up the letter we need.

So if we want to find the voltage then we write V equals

and then we cover up the V in the triangle.

That leaves us with I and R so we write I multiplied by which means voltage equals current multiplied by resistance.

You can write a little multiplication symbol in the triangle between the two letters if it helps you.

Now I know what you're thinking, why is current represented with the letter I and not a C for current,

or even a letter A for the unit of ampere?

Well the unit of current is the ampere or the amp, and this is named after André Ampere, a French physicist.

A couple of hundred years ago he undertook lots of experiments many involved varying the amount of electrical current.

So he called this intensity du current or the intensity of current.

So when he published his work they took the letter I and it became standard until this day.

Now you might also come across formulas where the letter E is used instead of V.

The letter E stands for EMF or electromotive force

but don't worry about that just stick to using V

and substitute V for E if you see it used in Ohm's law questions.

Anyway so by covering V we get voltage equals current multiplied by resistance.

If we want to find current then we write down I equals

and then we cover up the letter I in the triangle.

That gives us V and R

so as V is above the R like a fraction

we can write V divided by R therefore current is equal to voltage divided by resistance.

If we want to find resistance then we write down R equals and we cover up R in the triangle.

That leaves us with V and I so we write V divided by I

which gives us resistance equals voltage divided by current.

Let's look at some examples for how to use these formulas.

First let's see how we find voltage and how it relates to the other parts.

Let's say we have a simple electrical circuit with a battery and a resistor.

We don't know what the voltage of the battery is though.

The resistor is three ohms and when we connect a multimeter into the circuit, we see that we get a reading of two amps of current.

We want to find the voltage, so using ohms triangle, we can cover up the V and that gives us V equals I multiplied by R.

We know the current is two amps, so we can write that in, and we know the resistance is three ohms,

so we can write that in also.

Therefore, two amps multiplied by three ohms gives us six volts.

The battery is therefore 6 volts.

Now if you want to check your answers for ohms questions then I've built a free calculator on the website.

You can just drop your numbers in and it will do the calculation for you.

Links for that again in the video description down below.

Coming back to the circuit, if we now double the voltage by connecting two 6 volt batteries in series we get 12 volts.

If we now connect this to the same circuit the current also doubles from 2 amps to 4 amps.

If we double the voltage again to 24 volts, the current will also double to 8 amps.

So what's the relationship here?

We can see that current is therefore directly proportional to voltage.

If we double the voltage, we double the current.

Remember voltage is like pressure, is the pushing force in the circuit.

It pushes the electrons around the wires

and we place things like lamps in the way of these electrons

so that they have to flow through these and that causes the lamp to light up.

By doubling the voltage we see that the current also doubles,

meaning that more electrons are flowing and this occurs as we apply more pressure or more voltage.

This is just like if we were to use a bigger water pump then more water will flow.

Okay, so what about finding current?

Let's say we now have a 3 ohm lamp connected to a 6 volt power supply.

To find the current we write down I equals and then we cover up I in the triangle.

That gives us V divided by R, so current equals voltage divided by resistance.

We know the voltage is 6 volts and the resistance is 3 ohms, so the current is therefore 2 amps.

And that's what we see on the multimeter.

By the way, if you don't have a multimeter then I highly recommend you get one.

It's essential for troubleshooting but also building your essential electrical knowledge.

I'll leave some links down below for which one to get and from where.

So we saw what happens when we use a resistance of 3 ohms in the circuit.

But if we double the resistance to 6 ohms by placing another 3 ohm lamp into the circuit, the current halves to just 1 amp.

If we double the resistance again to 12 ohms, the current will half again to 0 .5 amps.

We can visually see this because the lamps will become less bright as the current reduces from the increase in resistance.

So what's the relationship here?

We can see that the current is inversely proportional to the resistance.

When we double the resistance the current will decrease by half.

If we half the resistance the current will double.

Current is the flow of electrons or the flow of free electrons.

For us to make this lamp shine we need to push electrons through it.

How do we do that?

We apply a voltage across the two ends.

The voltage will push the electrons.

The atoms inside the copper wire have free electrons in their valence shell

which means they can very easily move to other copper atoms.

They will naturally move to other atoms by themselves

but this will be in random directions which is of no use to us.

100

For the lamp to turn on we need lots of electrons to flow in the same direction.

101

When we connect to voltage source

102

we use the pressure of the battery to push the electrons through the circuit all in the same direction.

103

For example to power this 1 .5 ohm resistive lamp with a 1 .5 volt battery requires 1 amp of current.

104

This is equal to 6 ,242 ,000 ,000 electrons passing from the battery

105

and through the lamp every second and if we can achieve this then the lamp will stay at full brightness.

106

If the voltage or current reduces or the resistance of the circuit increases then the lamp will become dimmer.

107

Okay now let's look at finding resistance.

108

Say we have a resistive lamp connected to a 12 volt power supply.

109

We don't know how much resistance is adding to the circuit but we measure the current at 0 .5 amps.

110

To find the resistance we write down R equals and and then we cover up the R in the triangle.

111

We're left with V and I, so resistance equals voltage divided by current.

112

We know the voltage is 12 volts and the current is 0 .5 amps, so 12 divided by 0 .5 gives us 24 ohms of resistance.

113

Resistance is the opposition to the flow of electrons.

114

It tries to prevent electrons from flowing.

115

That's why we use resistors in circuits to reduce the current and protect components such as an LED.

116

If we try to connect an LED directly to a 9V battery, it will blow out because the voltage and the current are too high.

117

But when we add a resistor into the circuit, then these are reduced, so the LED is protected and will shine brightly.

118

So given the circuit, we can increase the current by increasing the voltage, or we can also increase the current by reducing the resistance.

119

We can also reduce the current by increasing the resistance.

120

Okay, time for you to test your skills.

121

Can you solve these problems?

122

I'll leave a link for the answer and the solution in the video description down below.

123

Problem one, let's say we have this lamp which has a resistance of 240 ohms.

124

If we plug this into an outlet in the US which uses 120 volts, what will the current be?

125

Problem two, if I plug the same 240 ohm resistive lamp into an outlet in the UK, we get a current of 0 .958 amps.

126

So what is the voltage being applied here?

127

Okay guys, that's it for this video, but to continue your learning,

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then check out one of the videos on screen now and I'll catch you there for the next lesson.

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Don't forget to follow us on Facebook, Twitter, Instagram, LinkedIn, as well as theengineeringmindset .com.

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このレッスンの語彙とスピーキングのポイント

このスピーキングレッスンは、動画「Ohms Law Explained - The basics circuit theory」を教材にしています。繰り返し出てくる語は次のとおりです：current, voltage, resistance, Amp, lamp。この動画には、シャドーイング用の文が108文、単語が1796語あります。音声の長さは9:49です。話す速さは速く、1分あたり約183語です。音のつながりや弱く発音される音が多くなります。英語の頻出3,000語に含まれる単語は80%だけなので、語彙は難しめです。

この動画の重要語彙

動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。

単語	発音	意味
voltage 名詞	/ˈvəʊltɪd͡ʒ/	電圧
lamp 名詞	/ˈlæ̝mp/	ランプ, 明かり
divide 動詞	/dɪˈvaɪd/	分割する, 分ける
triangle 名詞	/ˈtɹaɪˌæŋɡəl/	三角, 三角形
connect 動詞	/kəˈnɛkt/	繋げる
litter 名詞	/ˈlɪt.ɚ/	ごみ
formula 名詞	/ˈfɔː.mjʊ.lə/	公式, 定式
metre 名詞	/ˈmiːtəɹ/	メートル, ㍍
atom 名詞	/ˈætəm/	原子, アトム
wire 名詞	/ˈwaɪɚ/	針金, 線
solve 動詞	/sɒlv/	解決する
experiment 名詞	/ɪkˈspɛɹ.ə.mənt/	実験
copper 名詞	/ˈkɒpə/	銅, カッパー
relate 動詞	/ɹɪˈleɪt/	繋げる
leaf 名詞	/lif/	葉, 葉っぱ

動画に出てくる句動詞

単語	意味
write down 動詞	書き留める, 記す
check out 動詞	試験する, 検査する

この動画の文法

話し手がよく使っている文型を、動画の実際の表現とともに紹介します。

文型	動画での表現
受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる	was developed · can be found · is named
現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している	I've made · I've built
関係詞節 who / which + 節 — 人や物について情報を加える	directions which is · lamp which has

注意したい発音

話し手はdon't, I'll, I'veなど、短縮形や弱形を16回使っています。聞こえたとおりの短い形で発音しましょう。

「sh」と「zh」の音: shine /ʃaɪn/, shell /ʃɛl/, fraction /ˈfɹæk.ʃən/, calculation /ˌkælkjuˈleɪʃn̩/, multiplication /ˌmʌltɪplɪˈkeɪʃən/
長い単語（アクセントの位置に注意）: electrical /ɪˈlɛktɹɪkəl/, experiment /ɪkˈspɛɹ.ə.mənt/, naturally /ˈnæt͡ʃ.(ə.)ɹə.li/, intensity /ɪnˈtɛnsɪti/, visually /ˈvɪzju.əli/

日本語話者が苦手な音：

/r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: triangle /ˈtɹaɪˌæŋɡəl/, electrical /ɪˈlɛktɹɪkəl/, relate /ɹɪˈleɪt/, naturally /ˈnæt͡ʃ.(ə.)ɹə.li/, brightly /ˈbɹaɪtli/
/v/ — /b/ にならないように、上の歯を下唇に当てる: voltage /ˈvəʊltɪd͡ʒ/, divide /dɪˈvaɪd/, solve /sɒlv/, wherever /(h)wɛɹˈɛvɚ/, vary /ˈvɛəɹi/
/f/ — 「フ」ではなく、上の歯と下唇で出す: formula /ˈfɔː.mjʊ.lə/, leaf /lif/, forty /ˈfoɹti/, fraction /ˈfɹæk.ʃən/, physicist /ˈfɪzɪsɪst/

この動画での練習方法

まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
自分の声を録音して元の音声と比べます。voltage, lamp, divideなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →

シャドーイング練習: Ohms Law Explained - The basics circuit theory - 動画で英語スピーキングを学ぶ

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