Force on a current-carrying conductor in a magnetic field

0:00in a previous video we saw that if you run an electric current through a wire then it can deflect a magnetic needle kept close to it this means a current carrying wire can push on a magnet but Newton's third law says that for every action there must be an equal and opposite reaction so if a current carrying wire can push on a magnet then that means a magnet can also push on a current carrying wire so this wire must also experience a force due to this magnet and in this video we are going to explore the properties of this force well first let's think about how the why the magnet is pushing on the wire well remember how we said the wire was pushing on the magnet we said that whenever a wire carries current it

1:02produces its own magnetic field and we said it's that magnetic field that pushes this magnet now similarly how can we answer the question how does the magnet push on the wire we can say the magnet also produces its own magnetic fields let me get rid of the field of the wire and let me bring back that needle so the magnet also produces its own magnetic field which may look somewhat like this and it's that magnetic field that is pushing on this wire so this means in general we can say that whenever we have a current carrying wire or a current carrying conductor in a magnetic field it experiences a force so magnetic fields not only push magnets but they can also push current-carrying wires and that

2:05kind of makes sense because we've seen in previous videos that current-carrying wires sort of kind of behave like a magnet and so it makes sense that they would be affected by magnetic fields and this is awesome because now magnetic fields can push on current-carrying conductors and make them move this means we can now convert but you can now use electricity to make something move and this is the principle behind your electric fans or your electric cars or any electric machines where we use electricity to move something it is by using this principle you just place it in a magnetic field and the magnetic field will push that conductor but before we can do anything useful with this let's first learn the

2:58properties of this force like what does that force depend on what direction is that force acting over here things like that and so to figure this out people performed experiments in which they place this wire in a uniform magnetic field not like this a field where the field strength and the field Direction is same everywhere over the wire so that we can understand exactly how the field affects the wire you can see over here the field on this wire is not uniform its Direction is also continuously changing over the wire right so let's place the wire in a uniform magnetic field and see how it affects the wire so to produce a uniform magnetic field all we will need are two giant poles of a magnet and so now if we look at the

3:53field in between these two poles you may recall the field always starts from north and ends into the south outside the magnet the field will look somewhat like this and you can see that in this region the field is pretty uniform you can see the direction of the field is same everywhere and the field the crowdedness of the field lines is also same pretty much they are pretty much equidistant everywhere right so the field strength is also same everywhere over here and so now we can place a current carrying wire over here and for former experiment and if you're wondering how do we get to polls like this well then you can do two things either get to giant bar magnets one for this and one for that and keep it over

4:37here or we can use something called a horseshoe magnet which looks like a horseshoe which is shown over here and you can see the poles of a horseshoe magnet are apart just like what we need all right so now let's place our current-carrying wire in this magnetic field you can pass the current through it by attaching it to a battery which have not shown over here and then we can perform experiments and see what does that force depend on the first thing people wanted to check is how does the force depend on the strength of the current and I want you to sort of guess this what do you think will happen to the force acting on this wire if the strength of the current was to increase what do you expect well we know that a

5:28current carrying wire is sort of acting like a magnet and that's why it's being affected by the magnetic field right now if you increase the current then it will become sort of like a stronger magnet isn't it so you would expect the force to increase I think that's exactly what we found out we found out so this is a result number one from what experiment is that if you put more current through that wire it'll automatically experience more force so you can increase the force just by increasing the current if you decrease the current the force will decrease if you make the current zero the force will vanish the second result is not so obvious what they found is that the force acting on this wire not

6:13only depends on the current but it also depends upon the angle between the wire and the magnetic field what they found is that when that angle is perpendicular when the wire is perpendicular to the field like we have kept over here that's when the force is maximum so right now the force on this wire is max but if you were to keep our wire this way place the wire this way then you don't know the current is the same and everything else is the same turns out that the force will reduce because the angle has decreased this is very important and this is not at all obvious but experiments show us that and if you were to decrease this angle further the force will decrease just look at this angle angle between the

7:04wire and the field the force will keep on decreasing and eventually if the angle becomes zero if we make our wire parallel to the magnetic field the angle becomes zero the force vanishes the force becomes zero I've not written it down but we can remember this this is super important to remember so the force depends on the angle if it's zero the force is zero as the angle increases the force increases and when the angle reaches 90 degrees that's when the force turns out to be maximum the last thing we'll talk about is the direction of the force acting on this wire now we will figure out the direction of the force in a separate video all right we'll do that in complete detail in a separate video

7:56but the question over here is what do you think the direction of the force depends on again pause the video and think about this for a while all right well experiment shows us the direction of the force acting on this wire depends on two things it depends on the direction of the current in which direction the current is going so if the current is going upwards the direction of the force would be in one direction if the current is going downwards the direction of the force will reverse and it also depends upon the direction of the field if you reverse the field turns out again the direction of the force will reverse but don't worry too much about this Third Point as I said we will discuss about this in great detail in

8:44another video so what did we learn in this video we learned the current-carrying wire placed in a magnetic field experiences a force and using this we can now convert electricity to motion and we learned a couple of properties of this force we saw that more the force more more the current more the force and we also saw that the force is maximum when the wire is kept perpendicular to the direction of the field