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Current time:0:00Total duration:9:07

Video transcript

in a previous video we saw that a straight wire carrying an electric current produces magnetic fields which are in concentric circles in this video we will explore what do the magnetic field lines look like for a circular loop of wire carrying an electric current and a small spoiler alert' you may be familiar with these field patterns so to figure out the field pattern experimentally all we need to do is sprinkle some iron filings on top of it and that's what we will do first in this clip we have copper wires which are in a circle and notice these are made to pass through a glass slab inside this glass slab we have iron filings and so when we pass electric current through this it goes through the loop generates a magnetic field and then the iron filings will arrange themselves and they will reveal the pattern to us so here it is we have done the connection and now once we click on once we close the circuit the electric current will run through and we will see a pattern forming and there it is you can already see a pretty good pattern formed over there wow that's beautiful isn't it look at that alright so we can see that close to the wire the field is in circles but as you go farther away from the wire as we move towards the center notice the circle tends to become larger you tend to get a bigger curve look at the curve it tends to get bigger it tends to get flatter and then as we move towards the center of the loop notice it's pretty straight over here pretty straight so now let's try and figure out why the field looks like this and we'll see that this is actually a familiar field line we've seen this before so here is our copper ring it's a circle but we are looking at it from an angle like this and so it looks oval to us and let's say we put a current through it in this particular direction so the current is flowing this way into the board goes from the back outside the board comes out from the front and so on just like this goes here into the screen comes out from the back comes out and then goes on in circles how do we now figure out the direction of the magnetic field everywhere is the question well in a previous video we've seen that if you have straight wires then we can use the right-hand thumb rule basically take your right hand clasp that conductor says that the thumb points in the direction of the current then the four and circling fingers will give us the direction of the magnetic field and circling that straight wire and if you need more clarity on this we've discussed this in great detail in previous videos so feel free to go back and watch that video but here we don't have a straight wire we have a circle what do we do then how do we use our right hand thumb rule over here well all we have to do is clasp each section of this wire separately and figure out what the magnetic field looks like around that section so let's take an example imagine I want to know what the magnetic field looks like somewhere over here and I'm choosing this section of the wire because it's easier to draw the magnetic field on the screen as you will see so let's say at this section I want to know what the magnetic field looks like around that section then how do I do this well I have to clasp my right hand to this section so that the thumb points in the direction of the current but what direction is the current over here well since the current is moving to the right here it enters into the screen over here and so my thumb should point into the screen so let's see what it looks like if I were to clasp over there that's what it would look like you can't see my thumb because my thumb is pointing in to the screen and now the four and circling fingers give me the direction of the magnetic field around that section and notice the encircling fingers are running clockwise and so I know that around that section the magnetic field is going to be clockwise similarly if I consider now this section again I'm choosing that section because it's easy to draw the magnetic field over there you will see that the current is coming out of the screen over here it comes out and then goes to the right so if you're the class this section of the wire can you imagine what it would look like well this time with my right hand it should always be right hand my thumb should now point outwards outside the screen so if we clasp it with my right hand this is what it would look like and now that is the four and circling fingers are going anti-clockwise so I know the magnetic field around that section is going to be anti-clockwise so this explains the circular fields over here now to figure out the magnetic field everywhere else we don't have to keep doing this over and over again and make our job tedious instead there's an easy way to guess what the field might look like here's how I like to do it if you look over here it's telling us that the field inside the loop is pointing upwards outside downwards same thing over here even the field a root this section is telling us inside the loop is upwards outside the loop is downwards in fact regardless of which section you clasp you will find the field inside will be up and outside will be down so to convince you let me show you two more sections that we have clasped here they are we use the same right-hand thumb rule thumb points in the direction of the current and you can clearly see the four fingers are telling us inside the field is upwards outside downwards inside upwards outside downwards and so from this we know the field should start or inside should be up outside should be down and there should be closed loops we've studied that therefore all the field lines should go like this should go like this can you guess that can you see it now can you imagine it and so if we were to draw the complete picture let me get rid of these additional hands so that we can look at these field lines properly now if you look at all these field lines this is what it would look like so notice all of them the field is inside is up and they would tend to go down outside and this is exactly what we got in our experiment now the last thing I want to discuss is does this familiar this this feel look familiar to you and for that let me zoom out a little bit alright here it is look at this beautiful field pattern what does this resemble well this field looks very similar to that created by a tiny bar magnet we've seen what the field grade by a bar magnet looks like it looks somewhat like this now look at these two field patterns don't they look very similar to each other here also the field lines start from here and they continuously keep looping back like this here also the field lines start from here and they continuously keep looping back small difference you might see is over here the field is a little flatter and over here the feel is more round but if this bar magnet was very small if this bar magnet was very tiny then notice we would get a very very similar field like this so this means a current carrying loop resembles a tiny bar magnet and we can now say that this side represents the North Pole of that bar magnet and this side over here represent the South Pole the poles are not really there but if we think of it as a bar magnet we can treat it this way and this is pretty awesome because now we've learned how to create our own artificial bar magnets well tiny bar magnets and so in this video we learned how to figure out the magnetic field around the current can group using the same right-hand thumb rule and eventually we saw that a current carrying loop is equivalent to a tiny bar magnet