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Current time:0:00Total duration:9:06

Video transcript

in around 1820 a Dutch physicist named Hans Christian ørsted made an accidental discovery which opened up a whole new branch of physics that explored the connection between electricity and magnetism in this video we'll explore what this discovery was and what were its implications so as the story goes our start was doing a demonstration in his lecture in which he had a copper wire through which he would pass some electric current and on his table there happened to be a tiny magnetic compass there and what he found is when he ran an electric current through that wire to perform some experiment that magnetic compass deflected that's it this was the experiment that led to a great discovery now before we talk about what it was let's go ahead and repeat that experiment and so to perform this experiment all we need is a wire a battery to pass electric current through it and the magnetic needle once we connect this once we close the circuit a current will pass through it and just take a look at what happens to this magnetic needle all right here we go notice the magnetic needle deflected that's it that was the experiment now you may be thinking what's the big deal about this experiment so what well think about it so far we could use electricity to create heat or light but now for the very first time in the history of mankind we have discovered that electricity an electric current can make things turn can you imagine what could be the applications of that this principle is used in fans it's used in your washing machines in your electric drilling machines and so on it's the same principle on which our ammeter and voltmeter --zz work inside which you pass a current and there is a needle that deflects and shows us the reading but more importantly this experiment led us to a huge discovery what discovery you ask well let's think about this what can push on a magnetic compass magnetic fields we've seen before that magnets can create magnetic fields and when you bring a tiny compass in the vicinity of it the magnetic field pushes on that compass but over here there aren't any magnets nearby so who is creating a magnetic field that is deflecting this compass well because the electric current was responsible for this deflection maybe electric current produces a magnetic field around it and this was a huge discovery why was it huge oh because earlier we thought that electricity and magnetism were two completely separate phenomenon but now with this single experiment we are seeing that electric current is producing magnetic field which means this gives us a clue that there might be some connection between electricity and magnetism and that's why this opened up a whole new branch of science of branch of physics which we call electro magnetism in which we explore this connection between this electricity and magnetism so Erstad and probably some other physicists were pretty excited about this discovery they wanted to learn more about the connection between this electric current and its magnetic field so that's right doing they started doing more experiments with this one thing they immediately realized is that if you increase the strength of the current then the deflection in the needle also increased the compost deflected more this meant that the magnetic field got stronger so in other words they found out that if you put more current you automatically get more magnetic field try to make sense to me because it's the current that's producing the magnetic field so I would expect that if the current increases its effect would be more and as a result the field would also increase another thing that they found is if they keep the current the same but they keep this needle at different different places at different distances from the wire they found that the deflection was maximum close to the wire and as they move away from the wire the deflection became weaker and weaker smaller and smaller this meant that the magnetic field is very strong close to the wire but it weakens as we go farther away from the wire that's another result the field weakens with distance from the wire and again that kind of makes sense to me this is very similar to what happens close to a magnet if you are very close to a magnet its field is very strong its force is very strong and as you go far away from it the field weakens and finally they also want to learn what does the field look like what is the magnetic field lines look like and we've seen before to draw magnetic field lines all you have to do is sprinkle some iron filings and see how they arrange or keep this magnetic compass at different different places and look at how it Orient's so to do that they made this wire vertical and made it pass through some kind of a rectangular piece of cardboard on which you can sprinkle iron filings or you can put all your magnetic needles and when they place the needles they found out that the magnetic needles arrange themselves in this fashion the red represents the North Pole of the magnet and the blue is the South Pole now remember we define the direction of the magnetic field as a direction in which the North Pole points so over here the magnetic field is this way this means over here the magnetic field is this way and so on and so if we replace these needles with arrow marks that represent the direction of the magnetic field it would look somewhat like this can you see that these arrow marks are running in a circle and so if we draw a continuous line connecting these arrow marks we'll end up drawing a circle a circle centered at the wire and this means that if you want to find the direction of the magnetic field at any point around the wire you just draw a tangent to this circle so we draw a tangent to the circle here you get the magnetic field Direction here you draw a tangent to the circle there you get the magnetic field direction over there and of course we'll get more practice to this finding the direction of the magnetic field in another video but this is true at all distances even if I were to keep magnetic needles close by they would run in circles even farther away they would all run in circles and so the magnetic field everywhere around a straight wire carrying current would be in concentric circles so that's another result that we find the field lines are in concentric circles they all have a center at the wire and finally we also saw that the direction of this magnetic field lines depends on the direction of the current if we were to reverse the direction of the current the field lines would still be concentric but they will reverse their directions as well like this and also notice how we have drawn these field lines the circles are drawn close to each other near to the wire this is to indicate that the field is very strong close to the wire you may remember that one of the properties of the field lines are if the field if the field is stronger then we draw the field lines closer to each other and as we go away from the wire the field weakens and as a result we draw the circles farther away from each other so what did we learn in this video we learned that when you pass an electric current through any wire it produces a magnetic field around it this connected electricity and magnetism and with further experiments we explore the properties of these magnetic fields and we are not one important property we found is that the magnetic field lines due to a straight wire carrying current is going to be in concentric circles