Pratica di Shadowing: Basic Ohm's Law For Electricians - Impara a parlare inglese con i video

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So you need to learn Ohm's Law, but you're lost or have no idea where to start.

Don't panic, you've come to the right place.

In this video, we're going to simplify Ohm's Law for electricians.

Look at a demonstration and finally put the tires to the pavement and do some real calculations using what we've learned.

We'll cover series, parallel, and combination circuits in future installments.

Hey, my name is Dustin.

I'm a licensed master electrician.

I'm also a test prep and apprenticeship instructor.

Welcome to this episode of Smarter Sparky.

So what exactly is Ohm's Law?

To answer that question we have to acknowledge a problem with electricity.

We can't see it, we can't hear it, smell it, taste it or feel it.

Sure we can see lightning, we can hear thunder, and we can get zapped by electricity, right?

But those are all the observable effects from electricity, not the electricity itself.

So the problem with electricity is that it's very difficult to observe, but we can measure it.

The things that we can measure are voltage, current, and resistance.

These are the key players in the battle that is Ohm's law.

Let's take a look at the lineup.

Voltage is kind of like pressure.

Think of low pressure like low voltage and high pressure like high voltage.

It's how much force or more technically electromotive force, which is the technical definition of voltage, is available.

Voltage is symbolized by the letter E.

I know that's kind of weird.

Why isn't it the letter V, right?

It's because we use the letter V as our units, volts.

So that leaves us needing a different letter to symbolize the unknown value.

Therefore we use the letter E from electromotive force.

So for example E equals 12 volts.

Current is similar to flow rate or gallons per hour.

A garden hose is a relatively low gallons per minute so we could think of that as low current.

Whereas a river is moving lots of gallons per minute it would be thought of as a higher current.

Current is symbolized by the letter I for similar reasons as voltage right we need that different letter.

Current is measured in amperes or amps

so we use the letter A for the units

and symbolize it with the letter I which stands for intensity so for example I equals 4 amps.

Resistance is the final contender which can be thought of as a restriction in a water line.

The harder you squeeze a hose, the more the flow is restricted.

Resistance is measured in ohms.

It's symbolized by the letter R, which stands for resistance, and the value is symbolized by the uppercase omega symbol.

For example, R equals 8 ohms.

Resistance is all around us.

All wires have a natural resistance to them.

Bad connections act like a resistance, and we have to treat them as such.

We even have a component called a resistor that is an on-purpose resistance that can be added to a circuit.

Ohm's law is what relates all three of these items together.

Ohm's law states that voltage is equal to current times resistance.

This gives us the first formula, E equals I times R.

We can rearrange this formula and derive two additional formulas giving us a total of three Ohm's law formulas.

Here's the deal.

We don't have to memorize all three.

We can just remember the first one, E equals I times R.

By filling in this triangle, we can cover up the value that we want to solve for and get the resulting formula.

For example, we can cover up E, which leaves it next to IR.

When the leftover values are next to each other, that signifies multiplication.

So E equals I times R, the formula that we started with.

If we want to solve for current, we can simply cover up I, which leaves E over R.

That gives us I equals E divided by R, the second of our formulas.

Finally, we can solve for resistance by covering up R, which leaves E over I.

That gives us R equals E divided by I.

This trick is great for remembering Ohm's Law as you only need to memorize one formula.

You can simplify the triangle just by drawing a T bracket and filling in the values.

That's exactly what I did when I sat down to take my state exam.

Draw the little letter T and fill those values in.

then you've got that Ohm's law formula right there on your scratch paper.

I'm sure you guys have all seen this little cartoon before, something very similar.

It's a great graphical representation of how Ohm's law works.

Voltage or pressure is trying to push current or amps through a wire, pipe, but resistance is restricting how much can actually move.

Let's visualize this concept using the water pipe analogy we've been using.

Here we've got an aquarium pump and a length of tubing.

This hose clamp is going to act as our resistance.

With the clamp fully open and the pump running, we have our maximum current flow.

As the clamp is tightened down, increasing resistance, we can see the current flow decreases.

We get less water or current making it through the pipe.

Let's do a few practical Ohm's Law calculations, one for each of the three Ohm's Law equations.

Consider this circuit.

How much current would flow if we had a resistance of 6 ohms and a voltage of 12 volts?

So it looks like we need to solve for I which is our placeholder for current.

So let's grab our triangle and cover up the letter I and that leaves us with E over R, meaning I equals E divided by R.

Now it's just a matter of plugging the values in.

I equals 12 volts divided by 6 ohms.

12 divided by 6 is 2 amps.

See?

Easy peasy.

What about this circuit?

Now we know the voltage and current, but we don't know the resistance.

Let's grab our triangle and cover up the letter R.

That leaves us with E over I, meaning R equals E divided by I.

Simply plug our values from the diagram into the formula, which gives us R equals 24 volts divided by 6 amps, and we get a resistance of 4 ohms.

Finally, we have this example.

Now we know the current and the resistance, but we don't know what the applied voltage is.

Grabbing our triangle, we can cover up the letter E.

Remember E is voltage which gives us I right next to R meaning E equals I times R.

Plugging in our values we get E equals 5 amps times 8 ohms

and that calculates out to E our voltage equaling 40 volts.

Hey real quick getting noticed by the YouTube algorithm is nearly impossible these days without help from viewers like you.

If you like this teaching style and find this video helpful, please take a second to like and drop a comment.

It lets the algorithmic overlords know this content's worth sharing.

All right, back to the good stuff.

We've just talked about the three items that can be measured for Ohm's Law, voltage, current, and resistance.

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There's actually a fourth item as well, and that's power.

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Power is a unit of energy.

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We symbolize it using the letter P, and it's measured in watts.

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We use W as the units, watts.

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Basically power is the rate at which electrical work is performed.

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For example, a 60 watt light bulb does less work than a 100 watt light bulb.

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It puts out less light, less heat.

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The 100 watt light bulb puts out more light and more heat.

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There is another formula that concerns Watts law.

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Watts law states that power equals current times voltage or amps times volts.

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This formula is easy to remember because the variables spell out pi.

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Check it out.

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P equals I times E.

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Everybody likes pi, so it's easy to remember.

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Let's grab one of our previous examples.

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We calculated this first example to find out that the current was 2 amps.

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We can further calculate the power of this circuit by taking the current and multiplying it by the voltage.

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So the wattage of the load is going to be P equals 2 amps times 12 volts, or 24 watts.

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Just like Ohm's law, Watt's law has three different arrangements for the same formula.

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And just like Ohm's law, Watt's law can be put into a triangle to help us remember all of these formulas.

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Just remember pi and use that to fill in the triangle.

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Maybe you've seen a wheel like this before.

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Whether you have or not, it certainly looks intimidating.

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This wheel is called Ohm's wheel or Watt's wheel and it's actually pretty simple.

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The way the wheel works is we have four quadrants.

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Each quadrant calculates out one of the four items we can calculate.

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Voltage, current, resistance, and power.

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Each of the quadrants has three formulas within it.

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So taking E, voltage for example, E equals I times R, E equals P divided by I,

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and E also equals the square root of P times R.

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And it works that way for the other quadrants as well.

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Pretty neat, huh?

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This wheel actually has Ohm's law built within it.

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Here's E equals I times R, like we just saw.

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Here's I equals E divided by R, and here's R equals E divided by I.

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Watt's law is also in there.

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Here's pi, P equals I times E, and here's the other two formulas as well.

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Here's I equals P divided by E, and E equals P divided by I.

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So that leaves us with six remaining formulas.

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Where do those come from?

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These are derived formulas.

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Basically, they're an algebraic mashup of both Ohm's law and Watt's law.

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I'll show you one real quick example of where they come from, but don't worry about knowing this.

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It's only for the curious.

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For our example, let's take this formula here.

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E equals the square root of p times r.

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It's derived by taking the two formulas, i equals p divided by e, and i equals e divided by r.

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i is equal to i, therefore p divided by e has to be equal to e divided by r.

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If we cross multiply, we get e squared equals p times r.

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Take the square root of both sides to undo the square on the e, and we get e equals the square root of p times r.

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All the other formulas are calculated using the same algebraic concept.

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It combines Ohm's law and Watt's law to eliminate one of the variables.

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Make sure to watch the upcoming Ohm's law videos on series, parallel, and combination circuits,

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and I'm going to show you a way to solve them without actually really even needing these derived formulas.

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Links will be down in the description when they become available.

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Ohm's law doesn't have to be confusing.

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In a simple circuit there's only one voltage, one current, one resistance, and one power.

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When we get into series, parallel, and combination circuits we will have multiples of each value

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but I'll show you how to handle that when we get to that point.

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Just remember we really only need to memorize two formulas.

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E equals I times R and pi.

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P equals I times E.

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Then we can use triangles to solve for anything we need.

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If you want more practice with basic Ohm's Law, I have a free worksheet and answer key you can download.

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Links are down in the description.

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That wraps up basic Ohm's Law.

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Don't forget to feed the algorithm with all the things the algorithm praise.

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Like, comment, and a subscription if I have earned it.

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See you on the next one.

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Questo video contiene 168 frasi e 1967 parole da ripetere con lo shadowing. Il parlato dura 11:24. Chi parla ha un ritmo naturale di circa 173 parole al minuto, vicino a una conversazione quotidiana. Solo il 73% 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
formula sostantivo	/ˈfɔː.mjʊ.lə/	formula
voltage sostantivo	/ˈvəʊltɪd͡ʒ/	voltaggio, tensione
divide verbo	/dɪˈvaɪd/	dividere, dividersi
litter sostantivo	/ˈlɪt.ɚ/	lettiera
triangle sostantivo	/ˈtɹaɪˌæŋɡəl/	triangolo
watt sostantivo	/wɑt/	watt
leaf sostantivo	/lif/	foglia
solve verbo	/sɒlv/	risolvere
calculate verbo	/ˈkælkjʊleɪt/	calcolare
derive verbo	/dɪˈɹaɪv/	derivare
parallel aggettivo	/ˈpæ.ɹəˌlɛl/	parallelo
pipe sostantivo	/ˈpaɪp/	cornamusa
plug sostantivo	/plʌɡ/	spina
algorithm sostantivo	/ˈælɡəɹɪðm̩/	algoritmo
hose sostantivo	/hoʊz/	manichetta

I phrasal verb che sentirai

Parola	Significato
cover up verbo	insabbiare, occultare
find out verbo	scoprire
wrap up verbo	imballare, impacchettare

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	is symbolized · would be thought · is measured
Present perfect have/has + participio passato — un’azione passata che conta ancora adesso	you've come · we've learned · We've just talked
Frasi relative who / which + frase — un’informazione in più su una persona o una cosa	force, which is · contender which can

Pronuncia a cui fare attenzione

Chi parla usa 27 contrazioni e forme ridotte, come don't, I'm, we've. Pronunciale nella forma breve, così come le senti.

I suoni “th”: algorithm /ˈælɡəɹɪðm̩/, thunder /ˈθʌndɚ/, algorithmic /ˌælɡəˈɹɪðmɪk/
I suoni “sh” e “zh”: calculation /ˌkælkjuˈleɪʃn̩/, representation /ˌɹɛp.ɹə.zɛnˈteɪ.ʃən/, examination /ɪɡˌzæm.ɪˈneɪ.ʃən/, demonstration /dɛmənˈstɹeɪʃən/, subscription /səbˈskɹɪpʃən/
Parole lunghe — attenzione all’accento: electricity /ɪˌlɛkˈtɹɪsɪti/, electrical /ɪˈlɛktɹɪkəl/, representation /ˌɹɛp.ɹə.zɛnˈteɪ.ʃən/, examination /ɪɡˌzæm.ɪˈneɪ.ʃən/, eliminate /ɪˈlɪm.ɪ.neɪt/

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