跟读练习: Concept of Electric Current with Train example | TheElectricalGuy - 通过视频学习英语口语
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Hello everyone, in this video we are going to learn about all of these Topics.
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To understand what is electric current, it is very much important to understand what is atom and what is electron.
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So first we will learn about that and then we will learn about electric current with our simple train analogy.
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And this train example will make understanding of electric current very easy.
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So to get all of these details in the easiest way you need to watch the video.
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We have been listening right from our school that everything is made up of atoms.
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Our body, this ball, a wooden shit Everything that we see in our daily life is made up of small small atoms.
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As an electrical engineer, you may ask, why on earth I need to know about these atoms?
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But believe me, learning few basic things
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which I am going to tell you in next few minutes about atoms will help you to understand current
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and the materials from electrical perspective more easily.
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So moving on, every atom consists of three main parts i .e electrons, protons and neutrons.
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Thank you.
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Electrons has negative charge on them.
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Protons have positive charge on them and Neutron as the name suggests they are neutral
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which means they do not have any charge on them.
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In an atom, proton and neutrons are very tightly bounded together and this tight bounding is known as nucleus.
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As proton and neutron are very tightly bounded together, it is very difficult to add or remove any of the proton or neutron in an atom.
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Actually the total amount of proton in an atom decides its elemental identity.
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So if you can remove or add proton from an atom, you could actually change the type of metal.
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And by using this formula, you can convert any metal into gold.
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But we will leave that topic as that is not possible.
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Moving on, like proton it is also not possible to remove or add neutron in an atom.
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And adding or removing neutrons from an atom does not make any changes in its elemental identity.
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So don't try that too.
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However, electrons has freedom to move everywhere.
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They are like free birds, they can even go to another atom if pushed out and we can do that with very less energy.
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Electrons are like S -pole of a magnet and protons are like N -pole.
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As we know, two similar poles of a magnet repel each other but two different poles attract each other.
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and in similar way two particles with same charge will repel each other and particles with different charge will attract each other.
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To be more clear two electrons which are negatively charged will repel each other and in same way
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Two positively charged protons will repel each other.
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But, the interesting part is, like two different poles of magnet, two particles with different charge will attract each other.
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So negatively charged electrons are attracted towards the positively charged proton and vice versa.
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Now you may ask a question, if electrons and protons are attracted towards each other, then in an atom there would be always attraction and repulsion going on.
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The answer is no. To understand, look at this image carefully.
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The image shows the basic construction of an atom.
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Now, as you can see, there are four electrons and four protons are there in the above atom.
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So for understanding purpose we will consider charge on electrons equal to -4.
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as electrons are negatively charged and charge on proton are +4 as they are positively charged.
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So, to get the net charge we must add these two charges.
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So, +4 + -4 = 0.
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With this, we came to an important conclusion that equal amount of proton
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and electron in an atom cancel out the net charge and keeps the atom stable.
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Atom is stable only if the number of protons are equal to number of electrons.
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If I add or remove any electron from an atom, the atom will become unstable.
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and it is now ready to give or take the electrons to another unstable atom and become stable again.
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Let's say in our above atom I added one extra electron.
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Now the net charge is positive 4 plus negative 5.
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which is equal to -1.
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The net charge is not zero which means the atom is unstable.
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This atom will now try to lose one extra electron to another unstable atom and become stable again.
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We call such unstable atoms as charged atoms.
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Addition of electron in an atom makes it negatively charged and removal of electron from an atom makes it positively charged.
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The atom is like this train.
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In this condition the train is completely stable and not moving.
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But if we add batteries to it and turn on the switch the train becomes unstable and start moving.
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Now this train will keep on moving until the batteries gets dry completely or until we turn off the switch.
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Adding batteries to the train and turning on the switch is equivalent to adding an extra electron in an atom.
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As soon as we add battery and turn on the switch, the train starts and becomes unstable.
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And in similar way, as soon as we add extra electron in an atom, it becomes unstable and try to lose the required electron.
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Now let's learn about valence electron.
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Ladies and gentlemen, this is important to understand conductor, insulators and semiconductors.
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If you see this figure carefully, you will find that the atoms have different orbits which are shown by dotted lines.
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The electrons in the last orbit are known as valence electrons.
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The outermost orbit or also known as valence shell of an atom can have maximum 8 numbers of electrons.
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And, the number of electrons in outermost orbit of an atom decides the electrical property of the material.
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And hence, knowing this is important.
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If the atom has less than 4 electrons in its outermost orbit then the material can be used as a conductor.
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Examples are aluminium, copper etc. which has 3 and 1 electrons in their valence shell or the outermost orbit respectively.
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If the atom has more than 4 electrons in its outermost orbit, then the material can be used as an insulator.
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Nitrogen is one of the example of insulator which has 5 electrons in its outermost orbit.
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If the atom has exactly 4 electrons in its outermost orbit,
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then the material can be used as a semiconductor which has properties of both metal and nonmetal.
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Well if you know how many electrons are there in an outermost orbit of an atom,
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you also know if you can use that material as a conductor or as a insulator or maybe as a semiconductor.
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free electrons.
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The electrons in orbit near to the nucleus are tightly bounded to the nucleus.
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However, the electrons in the orbit
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which is away from the nucleus are loosely bounded with the nucleus as shown in the figure.
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We can relate this concept to the magnet and a pin.
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If the pin is near to the magnet it will experience more force
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and moving this pin away from the magnet will take some extra energy.
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But, if the pin is away from the magnet, the force will also be less
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and now we can move this pin with very less energy as compared to the previous case.
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In similar way, nucleus is like a magnet and electrons are like a pin.
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And therefore, electrons which are near to the nucleus will be tightly bounded and the electrons which are away from the nucleus,
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that is electrons in outermost orbit will be loosely bounded.
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And these loosely bounded electrons can be easily removed.
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We call such loosely bounded electrons as free electrons.
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if even if now you may think atom how many free free electrons are there
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but even if each atom gives one loosely bounded electrons we can get billions
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or maybe more of such free electrons from a Madal.
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good conductors of electricity.
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Material which has large number of free electrons are good conductors of electricity.
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Now if we make wire of such material and apply voltage across it, free electrons will start flowing from that material.
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And these are some good conductors of electricity.
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The best conductors of electricity are silver, copper, gold, aluminium in that order.
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It is important to know that not all the conductors of electricity provide same kind of conductivity.
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For example brass is also a conductor and silver is also a conductor.
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but the conductivity provided by silver is much greater than the conductivity provided by the brass.
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Since copper and aluminum is cheap and serve the purpose very well, it is used widely.
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In some cases silver plating is also done on a conductor to improve the conductivity.
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Now let's see the bad conductors of electricity or which is also called as insulators.
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Material which has very few or no free electrons are called as bad conductors of electricity or insulators.
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Even if you make wire of such material, no electricity will flow through it because it doesn't have any free electrons.
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Examples of insulators are like plastic,
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porcelain, glass, air etc. And But this insulator plays a very important role in many applications in electrical industry.
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For example, you can take cables which are present in our house.
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You can see that all the cables are insulated with plastic to avoid any direct contact with live conductor.
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And this insulator comes very handy saving so many lives every day.
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Now let's see about the semiconductors.
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There are few materials which has properties of both i .e conductor and insulator.
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At room temperature the material has very few free electrons and hence acts as an insulator.
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But if the temperature goes up to a certain limit, the material acts as a conductor.
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One example of semiconductor is silicon which is widely used in electronics devices.
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Yeah, so finally after learning the basics of atoms and electrons, it's time to learn about electric current.
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As we have seen, conductor which has free electrons can travel anywhere in the conductor if not directed.
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To understand what is electric current, let's get back to our train.
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This is our train and we want this train to go to the destination D.
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Well, if I start the train, train can go anywhere but not to the destination.
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But, if we place tracks from the initial position of the train to the destination D and turn on the train
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Now train will travel in the direction we want and it will reach to our destination D.
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Concept of electric current is not much different from this example.
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Tren represent the material filled with electrons.
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tracks is equivalent to the conductors and the batteries inside the trains is equivalent to the voltage source.
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The conductor has free electrons present in it.
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If these free electrons are not directed, it can move randomly in the conductor.
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But if we give them a direction and a path to flow, they flow in a coordinated fashion like our train travelled after placing the tracks.
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This directed flow of electron is what we call electric current.
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We can exactly relate this to our train example.
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The example makes the understanding of electric current much easier, isn't it?
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This uniform flow of electrons is what we call as electricity or electric current.
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Yes, it is as simple as that.
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You can consider a copper strip as shown in this figure.
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If we apply voltage to it, negatively charged free electron starts flowing towards the positive terminal.
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This directed flow of electron is what we call electric current.
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From this figure you can see
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that the direction of current is from negative terminal to positive terminal and which is correct as well.
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And this direction of current is called as actual direction of current.
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However, it was assumed that the current flowed from positive terminal to the negative terminal via conductors
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and this assumption is so firmly established that it is still in use.
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And this direction is what we call conventional direction of conductors current Of course,
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now we need a unit to measure the current flowing from a circuit or a closed network.
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Now, someone may say very large current is flowing through the circuit or very small current is flowing through the circuit but,
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How do we know if the flowing current is large or small?
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It is simple too.
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More electrons flows per second we can say current is large
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and when very few electron flows per second we can say current is small.
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The strength of electric current is electrons flowing per second, that is charge flowing per second.
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The unit of charge is coulomb which is represented by letter c.
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1 coulomb indicates charge on 625 multiplied by 10 to the power 16 electrons.
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My god that's huge isn't it.
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So 1 coulomb is equal to charge on 625 multiplied by 10 to the power 16 electrons.
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So the current
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The charge queue is measured in coulombs
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and the time is measured in seconds and hence the unit of current will be coulombs per second or ampere.
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If charge is equal to 1 coulomb
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and time is equal to 1 second then we can say that 1 ampere of current is flowing.
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If someone says current of 5A is flowing then it is basically 5 coulombs of charge flowing per second through the wire.
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And 5 coulombs indicates charge on 5 multiplied by 625 multiplied by 10 to the power 16 electrons.
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So if you want to increase the current flowing through a wire, you have to increase charge flowing per second.
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So, the unit of current is ampere or coulmbs per second.
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Ampere is most commonly used.
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Now let's see about the types of electric current.
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We can divide electric current in two main types.
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First is steady state current or direct current.
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When the magnitude
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or the amount of current does not changes with time as shown in the figure we call it steady state
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or direct current or in short DC.
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As you can see from figure current remains the same as the time changes.
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Current provided by batteries is direct current and it remains almost constant.
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The second type is alternating current.
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When current changes its magnitude and direction with time, then it is called as alternating current or AC in short.
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As you can see in this image, magnitude and direction of the current is changing with time.
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The current is flowing in alternate direction, half time it is in positive side and for the half time it is in negative side.
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And hence we call it alternating current.
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The current generated by generators in power station is alternating current or AC.
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So that was it for this video, in next video we will learn how we can make electrons to flow, we will learn about voltage.
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If you like the video do share it with your friends
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and do subscribe to my channel to get more such easy to understand videos.
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That's all for this video guys, I'll see you in my next one but till then,
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Keep watching, keep learning.
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本课的词汇与口语要点
这段视频共有 183 个句子、2520 个单词可供跟读。 讲话部分时长为 18:07。 说话人语速平稳，每分钟约 139 个词，很适合跟读。 只有 80% 的单词属于英语最常用的 3,000 词，词汇难度较高。
视频中的重点词汇
视频中 15 个值得学习的单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| atom 名词 | /ˈætəm/ | 原子 |
| conductor 名词 | /kənˈdʌktɚ/ | 指揮 /指挥, 指揮家 /指挥家 |
| electron 名词 | /ɪˈlɛk.tɹɑn/ | 電子 /电子 |
| orbit 名词 | /ˈɔɹ.bɪt/ | 軌道 /轨道, 軌跡 /轨迹 |
| magnet 名词 | /ˈmæɡ.nɪt/ | 磁鐵 /磁铁, 磁石 |
| nucleus 名词 | /ˈnuː.kli.əs/ | 核心, 核 |
| stable 名词 | /ˈsteɪ.bəl/ | 馬厩, 馬棚 /马棚 |
| terminal 名词 | /ˈtɚmɪnəl/ | 航站, 航廈 /航厦 |
| pole 名词 | /pəʊl/ | 極 /极 |
| attract 动词 | /əˈtɹækt/ | 吸引 |
| semiconductor 名词 | /ˌsɛmikənˈdʌktə/ | 半導體 /半导体 |
| wire 名词 | /ˈwaɪɚ/ | 線 /线, 鐵絲 /铁丝 |
| hence 副词 | /ˈhɛns/ | 從這裡 /从这里, 從這兒 /从这儿 |
| copper 名词 | /ˈkɒpə/ | 銅 /铜 |
| destination 名词 | /dɛstɪˈneɪʃən/ | 目的地 |
视频中出现的短语动词
| 单词 | 释义 |
|---|---|
| turn off 动词 | 關 /关, 關掉 /关掉 |
需要注意的发音
说话人用了 5 次缩略和弱读形式，例如 isn't, doesn't, don't。请按听到的简短形式来说。
- “sh” 和 “zh” 音: destination /dɛstɪˈneɪʃən/, shell /ʃɛl/, establish /ɪˈstæb.lɪʃ/, conclusion /kənˈkluːʒən/, conventional /kənˈvɛnʃənl̩/
- 长单词——注意重音位置: electricity /ɪˌlɛkˈtɹɪsɪti/, semiconductor /ˌsɛmikənˈdʌktə/, electrical /ɪˈlɛktɹɪkəl/, destination /dɛstɪˈneɪʃən/, positively /ˈpɑ.zɪ.tɪv.li/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 用正常速度逐句跟读，每句重复到你的节奏与说话人一致为止。
- 录下自己的声音并与原声对比，特别注意 atom, conductor, electron 这类单词。
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | is made · is known · are attracted |
| 定语从句 who / which + 从句 — 补充说明人或事物 | electrons which are · zero which means · orbits which are |
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。