Pratica di Shadowing: Ohms Law Explained - The basics circuit theory - Impara a parlare inglese con i video
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Hey there guys, Paul here from theengineeringmindset .com.
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In this video we're going to be looking at Ohm's Law
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to understand how it works as well as how to use it.
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There are also two problems at the end of this video for you to test your knowledge
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and see if you can solve.
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So what is Ohm's Law?
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Ohm's Law is the relationship between voltage, current and resistance and how they relate to each other.
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Ohm's law was developed by a German physicist named George Ohm
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who undertook many experiments to develop his theory including measuring current by touching live electrical circuits to see how much it hurt.
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As you might imagine the higher the current the more it hurt.
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Now there are three formulas we need to use for Ohm's law
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but we don't actually need to remember these and I'll show you a super easy tip in just a moment.
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So the three formulas we use for Ohm's law are voltage equals current multiplied by resistance, current equals voltage divided by resistance,
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and resistance equals voltage divided by current.
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If that seems like a lot to remember then don't worry because we don't need to remember them.
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All we need to remember is Ohm's triangle which looks like this.
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So you just need to remember these three letters in order V, I, R.
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Then we just write those letters in a triangle with V at the top
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and we draw a line to separate the letters.
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In fact you don't even need to remember those
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because I've made a free PDF guide for you with some worked examples
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which you can keep on your PC or your mobile and access wherever you need.
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Links for that can be found in the video description down below.
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Now all we do when we need to use a formula is cover up the letter we need.
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So if we want to find the voltage then we write V equals
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and then we cover up the V in the triangle.
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That leaves us with I and R so we write I multiplied by which means voltage equals current multiplied by resistance.
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You can write a little multiplication symbol in the triangle between the two letters if it helps you.
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Now I know what you're thinking, why is current represented with the letter I and not a C for current,
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or even a letter A for the unit of ampere?
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Well the unit of current is the ampere or the amp, and this is named after André Ampere, a French physicist.
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A couple of hundred years ago he undertook lots of experiments many involved varying the amount of electrical current.
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So he called this intensity du current or the intensity of current.
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So when he published his work they took the letter I and it became standard until this day.
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Now you might also come across formulas where the letter E is used instead of V.
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The letter E stands for EMF or electromotive force
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but don't worry about that just stick to using V
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and substitute V for E if you see it used in Ohm's law questions.
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Anyway so by covering V we get voltage equals current multiplied by resistance.
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If we want to find current then we write down I equals
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and then we cover up the letter I in the triangle.
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That gives us V and R
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so as V is above the R like a fraction
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we can write V divided by R therefore current is equal to voltage divided by resistance.
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If we want to find resistance then we write down R equals and we cover up R in the triangle.
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That leaves us with V and I so we write V divided by I
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which gives us resistance equals voltage divided by current.
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Let's look at some examples for how to use these formulas.
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First let's see how we find voltage and how it relates to the other parts.
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Let's say we have a simple electrical circuit with a battery and a resistor.
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We don't know what the voltage of the battery is though.
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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.
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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.
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We know the current is two amps, so we can write that in, and we know the resistance is three ohms,
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so we can write that in also.
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Therefore, two amps multiplied by three ohms gives us six volts.
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The battery is therefore 6 volts.
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Now if you want to check your answers for ohms questions then I've built a free calculator on the website.
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You can just drop your numbers in and it will do the calculation for you.
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Links for that again in the video description down below.
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Coming back to the circuit, if we now double the voltage by connecting two 6 volt batteries in series we get 12 volts.
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If we now connect this to the same circuit the current also doubles from 2 amps to 4 amps.
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If we double the voltage again to 24 volts, the current will also double to 8 amps.
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So what's the relationship here?
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We can see that current is therefore directly proportional to voltage.
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If we double the voltage, we double the current.
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Remember voltage is like pressure, is the pushing force in the circuit.
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It pushes the electrons around the wires
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and we place things like lamps in the way of these electrons
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so that they have to flow through these and that causes the lamp to light up.
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By doubling the voltage we see that the current also doubles,
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meaning that more electrons are flowing and this occurs as we apply more pressure or more voltage.
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This is just like if we were to use a bigger water pump then more water will flow.
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Okay, so what about finding current?
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Let's say we now have a 3 ohm lamp connected to a 6 volt power supply.
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To find the current we write down I equals and then we cover up I in the triangle.
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That gives us V divided by R, so current equals voltage divided by resistance.
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We know the voltage is 6 volts and the resistance is 3 ohms, so the current is therefore 2 amps.
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And that's what we see on the multimeter.
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By the way, if you don't have a multimeter then I highly recommend you get one.
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It's essential for troubleshooting but also building your essential electrical knowledge.
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I'll leave some links down below for which one to get and from where.
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So we saw what happens when we use a resistance of 3 ohms in the circuit.
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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.
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If we double the resistance again to 12 ohms, the current will half again to 0 .5 amps.
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We can visually see this because the lamps will become less bright as the current reduces from the increase in resistance.
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So what's the relationship here?
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We can see that the current is inversely proportional to the resistance.
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When we double the resistance the current will decrease by half.
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If we half the resistance the current will double.
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Current is the flow of electrons or the flow of free electrons.
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For us to make this lamp shine we need to push electrons through it.
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How do we do that?
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We apply a voltage across the two ends.
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The voltage will push the electrons.
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The atoms inside the copper wire have free electrons in their valence shell
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which means they can very easily move to other copper atoms.
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They will naturally move to other atoms by themselves
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but this will be in random directions which is of no use to us.
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For the lamp to turn on we need lots of electrons to flow in the same direction.
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When we connect to voltage source
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we use the pressure of the battery to push the electrons through the circuit all in the same direction.
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For example to power this 1 .5 ohm resistive lamp with a 1 .5 volt battery requires 1 amp of current.
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This is equal to 6 ,242 ,000 ,000 electrons passing from the battery
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and through the lamp every second and if we can achieve this then the lamp will stay at full brightness.
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If the voltage or current reduces or the resistance of the circuit increases then the lamp will become dimmer.
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Okay now let's look at finding resistance.
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Say we have a resistive lamp connected to a 12 volt power supply.
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We don't know how much resistance is adding to the circuit but we measure the current at 0 .5 amps.
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To find the resistance we write down R equals and and then we cover up the R in the triangle.
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We're left with V and I, so resistance equals voltage divided by current.
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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.
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Resistance is the opposition to the flow of electrons.
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It tries to prevent electrons from flowing.
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That's why we use resistors in circuits to reduce the current and protect components such as an LED.
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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.
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But when we add a resistor into the circuit, then these are reduced, so the LED is protected and will shine brightly.
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So given the circuit, we can increase the current by increasing the voltage, or we can also increase the current by reducing the resistance.
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We can also reduce the current by increasing the resistance.
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Okay, time for you to test your skills.
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Can you solve these problems?
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I'll leave a link for the answer and the solution in the video description down below.
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Problem one, let's say we have this lamp which has a resistance of 240 ohms.
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If we plug this into an outlet in the US which uses 120 volts, what will the current be?
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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.
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So what is the voltage being applied here?
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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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Vocabolario e note di pronuncia per questa lezione
Questa lezione di conversazione si basa sul video “Ohms Law Explained - The basics circuit theory”. Le parole che ritornano più spesso: current, voltage, resistance, Amp, lamp. Questo video contiene 108 frasi e 1796 parole da ripetere con lo shadowing. Il parlato dura 9:49. Chi parla va veloce, circa 183 parole al minuto: aspettati suoni legati e ridotti. Solo il 80% delle parole rientra nelle 3.000 più comuni dell’inglese, quindi il lessico è impegnativo.
Vocaboli chiave di questo video
15 parole del video che vale la pena imparare, con pronuncia e significato:
| Parola | Pronuncia | Significato |
|---|---|---|
| voltage sostantivo | /ˈvəʊltɪd͡ʒ/ | voltaggio, tensione |
| lamp sostantivo | /ˈlæ̝mp/ | lampada, lampadina |
| divide verbo | /dɪˈvaɪd/ | dividere, dividersi |
| triangle sostantivo | /ˈtɹaɪˌæŋɡəl/ | triangolo |
| connect verbo | /kəˈnɛkt/ | connettere, connettersi |
| litter sostantivo | /ˈlɪt.ɚ/ | lettiera |
| formula sostantivo | /ˈfɔː.mjʊ.lə/ | formula |
| metre sostantivo | /ˈmiːtəɹ/ | metro |
| atom sostantivo | /ˈætəm/ | atomo |
| wire sostantivo | /ˈwaɪɚ/ | filo, filo metallico |
| solve verbo | /sɒlv/ | risolvere |
| experiment sostantivo | /ɪkˈspɛɹ.ə.mənt/ | esperimento |
| copper sostantivo | /ˈkɒpə/ | rame |
| relate verbo | /ɹɪˈleɪt/ | riferire |
| leaf sostantivo | /lif/ | foglia |
I phrasal verb che sentirai
| Parola | Significato |
|---|---|
| cover up verbo | insabbiare, occultare |
| write down verbo | sottoscrivere, annotare |
| check out verbo | investigare |
| come across verbo | dare l'impressione, avere l'aria |
La grammatica di questo video
Le strutture che chi parla usa di più, con le parole esatte del video:
| Struttura | Nel video |
|---|---|
| Forma passiva be + participio passato — conta ciò che accade, non chi lo fa | was developed · can be found · is named |
| Present perfect have/has + participio passato — un’azione passata che conta ancora adesso | I've made · I've built |
| Frasi relative who / which + frase — un’informazione in più su una persona o una cosa | directions which is · lamp which has |
Pronuncia a cui fare attenzione
Chi parla usa 16 contrazioni e forme ridotte, come don't, I'll, I've. Pronunciale nella forma breve, così come le senti.
- I suoni “sh” e “zh”: shine /ʃaɪn/, shell /ʃɛl/, fraction /ˈfɹæk.ʃən/, calculation /ˌkælkjuˈleɪʃn̩/, multiplication /ˌmʌltɪplɪˈkeɪʃən/
- Parole lunghe — attenzione all’accento: electrical /ɪˈlɛktɹɪkəl/, experiment /ɪkˈspɛɹ.ə.mənt/, naturally /ˈnæt͡ʃ.(ə.)ɹə.li/, intensity /ɪnˈtɛnsɪti/, visually /ˈvɪzju.əli/
I suoni difficili per chi parla italiano:
- Consonante finale — senza aggiungere una vocale dopo: voltage /ˈvəʊltɪd͡ʒ/, circuit /ˈsɝ.kɪt/, lamp /ˈlæ̝mp/, divide /dɪˈvaɪd/, connect /kəˈnɛkt/
- /æ/ — più aperta della “e”: lamp /ˈlæ̝mp/, triangle /ˈtɹaɪˌæŋɡəl/, atom /ˈætəm/, naturally /ˈnæt͡ʃ.(ə.)ɹə.li/, fraction /ˈfɹæk.ʃən/
Come esercitarsi con questo video
- Ascolta tutto il video una volta senza parlare e annota le parole che non conosci.
- Inizia a velocità 0,75×, fai shadowing frase per frase e torna alla velocità normale quando diventa facile.
- Registrati e confronta con l’originale, facendo attenzione a parole come voltage, lamp, divide.
Cos'è la tecnica dello Shadowing?
Shadowing è una tecnica di apprendimento delle lingue supportata da studi scientifici, originariamente sviluppata per la formazione dei traduttori professionisti e resa popolare dal poliglotta Dr. Alexander Arguelles. Il metodo è semplice ma potente: ascolti un audio in inglese di madrelingua e lo ripeti immediatamente ad alta voce — come un'ombra che segue il parlante con un ritardo di solo 1–2 secondi. A differenza dell'ascolto passivo o degli esercizi di grammatica, lo shadowing costringe il tuo cervello e i muscoli della bocca a elaborare e riprodurre simultaneamente i modelli di discorso reale. La ricerca dimostra che migliora significativamente la precisione della pronuncia, l'intonazione, il ritmo, il discorso connesso, la comprensione dell'ascolto e la fluidità del parlato — rendendolo uno dei metodi più efficaci per la preparazione alla prova di speaking dell'IELTS e per la comunicazione reale in inglese.