跟讀練習: Basic Ohm's Law For Electricians - 通過影片學習英語口語
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So you need to learn Ohm's Law, but you're lost or have no idea where to start.
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Don't panic, you've come to the right place.
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In this video, we're going to simplify Ohm's Law for electricians.
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Look at a demonstration and finally put the tires to the pavement and do some real calculations using what we've learned.
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We'll cover series, parallel, and combination circuits in future installments.
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Hey, my name is Dustin.
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I'm a licensed master electrician.
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I'm also a test prep and apprenticeship instructor.
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Welcome to this episode of Smarter Sparky.
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So what exactly is Ohm's Law?
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To answer that question we have to acknowledge a problem with electricity.
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We can't see it, we can't hear it, smell it, taste it or feel it.
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Sure we can see lightning, we can hear thunder, and we can get zapped by electricity, right?
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But those are all the observable effects from electricity, not the electricity itself.
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So the problem with electricity is that it's very difficult to observe, but we can measure it.
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The things that we can measure are voltage, current, and resistance.
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These are the key players in the battle that is Ohm's law.
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Let's take a look at the lineup.
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Voltage is kind of like pressure.
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Think of low pressure like low voltage and high pressure like high voltage.
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It's how much force or more technically electromotive force, which is the technical definition of voltage, is available.
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Voltage is symbolized by the letter E.
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I know that's kind of weird.
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Why isn't it the letter V, right?
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It's because we use the letter V as our units, volts.
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So that leaves us needing a different letter to symbolize the unknown value.
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Therefore we use the letter E from electromotive force.
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So for example E equals 12 volts.
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Current is similar to flow rate or gallons per hour.
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A garden hose is a relatively low gallons per minute so we could think of that as low current.
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Whereas a river is moving lots of gallons per minute it would be thought of as a higher current.
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Current is symbolized by the letter I for similar reasons as voltage right we need that different letter.
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Current is measured in amperes or amps
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so we use the letter A for the units
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and symbolize it with the letter I which stands for intensity so for example I equals 4 amps.
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Resistance is the final contender which can be thought of as a restriction in a water line.
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The harder you squeeze a hose, the more the flow is restricted.
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Resistance is measured in ohms.
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It's symbolized by the letter R, which stands for resistance, and the value is symbolized by the uppercase omega symbol.
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For example, R equals 8 ohms.
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Resistance is all around us.
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All wires have a natural resistance to them.
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Bad connections act like a resistance, and we have to treat them as such.
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We even have a component called a resistor that is an on-purpose resistance that can be added to a circuit.
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Ohm's law is what relates all three of these items together.
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Ohm's law states that voltage is equal to current times resistance.
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This gives us the first formula, E equals I times R.
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We can rearrange this formula and derive two additional formulas giving us a total of three Ohm's law formulas.
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Here's the deal.
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We don't have to memorize all three.
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We can just remember the first one, E equals I times R.
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By filling in this triangle, we can cover up the value that we want to solve for and get the resulting formula.
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For example, we can cover up E, which leaves it next to IR.
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When the leftover values are next to each other, that signifies multiplication.
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So E equals I times R, the formula that we started with.
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If we want to solve for current, we can simply cover up I, which leaves E over R.
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That gives us I equals E divided by R, the second of our formulas.
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Finally, we can solve for resistance by covering up R, which leaves E over I.
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That gives us R equals E divided by I.
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This trick is great for remembering Ohm's Law as you only need to memorize one formula.
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You can simplify the triangle just by drawing a T bracket and filling in the values.
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That's exactly what I did when I sat down to take my state exam.
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Draw the little letter T and fill those values in.
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then you've got that Ohm's law formula right there on your scratch paper.
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I'm sure you guys have all seen this little cartoon before, something very similar.
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It's a great graphical representation of how Ohm's law works.
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Voltage or pressure is trying to push current or amps through a wire, pipe, but resistance is restricting how much can actually move.
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Let's visualize this concept using the water pipe analogy we've been using.
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Here we've got an aquarium pump and a length of tubing.
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This hose clamp is going to act as our resistance.
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With the clamp fully open and the pump running, we have our maximum current flow.
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As the clamp is tightened down, increasing resistance, we can see the current flow decreases.
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We get less water or current making it through the pipe.
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Let's do a few practical Ohm's Law calculations, one for each of the three Ohm's Law equations.
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Consider this circuit.
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How much current would flow if we had a resistance of 6 ohms and a voltage of 12 volts?
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So it looks like we need to solve for I which is our placeholder for current.
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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.
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Now it's just a matter of plugging the values in.
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I equals 12 volts divided by 6 ohms.
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12 divided by 6 is 2 amps.
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See?
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Easy peasy.
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What about this circuit?
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Now we know the voltage and current, but we don't know the resistance.
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Let's grab our triangle and cover up the letter R.
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That leaves us with E over I, meaning R equals E divided by I.
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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.
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Finally, we have this example.
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Now we know the current and the resistance, but we don't know what the applied voltage is.
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Grabbing our triangle, we can cover up the letter E.
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Remember E is voltage which gives us I right next to R meaning E equals I times R.
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Plugging in our values we get E equals 5 amps times 8 ohms
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and that calculates out to E our voltage equaling 40 volts.
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Hey real quick getting noticed by the YouTube algorithm is nearly impossible these days without help from viewers like you.
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If you like this teaching style and find this video helpful, please take a second to like and drop a comment.
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It lets the algorithmic overlords know this content's worth sharing.
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All right, back to the good stuff.
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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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本課的詞彙與口語要點
這段影片共有 168 個句子、1967 個單詞可供跟讀。 講話部分時長為 11:24。 說話人語速自然，每分鐘約 173 個詞，接近日常對話。 只有 73% 的單詞屬於英語最常用的 3,000 詞，詞彙難度較高。
影片中的重點詞彙
影片中 15 個值得學習的單詞，附發音和釋義：
| 單詞 | 發音 | 釋義 |
|---|---|---|
| formula 名詞 | /ˈfɔː.mjʊ.lə/ | 公式 |
| voltage 名詞 | /ˈvəʊltɪd͡ʒ/ | 電壓 /電壓 |
| divide 動詞 | /dɪˈvaɪd/ | 分, 分裂 |
| litter 名詞 | /ˈlɪt.ɚ/ | 墊料 |
| triangle 名詞 | /ˈtɹaɪˌæŋɡəl/ | 三角, 三角形 |
| watt 名詞 | /wɑt/ | 瓦特 |
| leaf 名詞 | /lif/ | еезы, еер |
| solve 動詞 | /sɒlv/ | 解決 /解決 |
| calculate 動詞 | /ˈkælkjʊleɪt/ | 計算 /計算, 算 |
| parallel 形容詞 | /ˈpæ.ɹəˌlɛl/ | 平行的 |
| pipe 名詞 | /ˈpaɪp/ | 笛子, 管子 |
| plug 名詞 | /plʌɡ/ | 插頭 /插頭 |
| algorithm 名詞 | /ˈælɡəɹɪðm̩/ | 演算法, 演算法 |
| gallon 名詞 | /ˈɡælən/ | 加侖 /加侖 |
| hose 名詞 | /hoʊz/ | 軟管 /軟管, 水龍帶 /水龍帶 |
影片中出現的短語動詞
| 單詞 | 釋義 |
|---|---|
| cover up 動詞 | 掩蓋 /掩蓋, 掩飾 /掩飾 |
| find out 動詞 | 找出, 查明 |
影片中的語法
說話人最常用的結構，並附上影片中的原話：
| 結構 | 影片中的用法 |
|---|---|
| 被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的 | is symbolized · would be thought · is measured |
| 現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事 | you've come · we've learned · We've just talked |
| 定語從句 who / which + 從句 — 補充說明人或事物 | force, which is · contender which can |
需要注意的發音
說話人用了 27 次縮略和弱讀形式，例如 don't, I'm, we've。請按聽到的簡短形式來說。
- “th” 音: algorithm /ˈælɡəɹɪðm̩/, thunder /ˈθʌndɚ/, algorithmic /ˌælɡəˈɹɪðmɪk/
- “sh” 和 “zh” 音: calculation /ˌkælkjuˈleɪʃn̩/, representation /ˌɹɛp.ɹə.zɛnˈteɪ.ʃən/, examination /ɪɡˌzæm.ɪˈneɪ.ʃən/, demonstration /dɛmənˈstɹeɪʃən/, subscription /səbˈskɹɪpʃən/
- 長單詞——注意重音位置: electricity /ɪˌlɛkˈtɹɪsɪti/, electrical /ɪˈlɛktɹɪkəl/, representation /ˌɹɛp.ɹə.zɛnˈteɪ.ʃən/, examination /ɪɡˌzæm.ɪˈneɪ.ʃən/, eliminate /ɪˈlɪm.ɪ.neɪt/
如何用這段影片練習
- 先完整聽一遍影片，不要開口，記下不認識的單詞。
- 先用 0.75 倍速逐句跟讀，熟練之後再回到正常速度。
- 錄下自己的聲音並與原聲對比，特別注意 formula, voltage, divide 這類單詞。
什麼是跟讀法？
跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。