[Music] I'm welcome back to free size lessons Kol UK by the end of this video you should be able to describe what's meant by the ball to effect you should then be able to calculate the size of the force generated by the mode to effect and finally you should be able to determine the direction of the force by using Fleming's left hand rule and all of this is for high-tier students only in a previous video we saw that a magnetic field is produced when a current moves through a wire so the question is what would happen if we place this wire in another magnetic field I'm showing you here a wire carrying an electric current the arrow shows the direction of the conventional current remember that there's a magnetic field around this wire but we're not showing it we've now placed the wire into a magnetic field the magnetic field around the wire now interacts with the magnetic field between the magnets this means that the wire now experiences a force in this case the force is in the upward direction this force would cause a wire to move upwards scientists call this the motor effect and you could be asked that in your exam we can calculate the size of the force using this equation the force in Newton's equals the magnetic flux density in Tesla multiplied by the current in amperes multiplied by the length of the wire in meters and you are given this equation in the exam so you don't need to learn it now there are a couple of points about this equation firstly this applies to a wire which is at right angles to the magnetic field secondly the magnetic flux density is a measure of the strength of the magnetic field here's a sample question for you a wire has a length of 2.5 meters and is carrying a count of 1.5 ohm pairs the magnetic flux density is naught point naught 5 Tesla calculate the force acting on the wire so pause the video and try this yourself ok as we said before the force equals a magnetic flux density multiplied by the current multiplied by the length the magnetic flux density is naught point naught 5 Tesla the current is 1.5 pears and the length is 2.5 meters putting these into the equation it gives us a force acting on the wire of noir point one nine Newtons to two decimal places now in the exam you could be asked to name the factors that affect the size of the force looking again at the equation we can see that the force depends on three factors the magnetic flux density a current and the length of the conductor okay going back to our diagram as we saw the wire is experiencing a force we're going to look now how to determine the direction of the force to do that we use Fleming's left hand rule here's how we do it place your thumb first finger on 2nd finger so there were right angles like this now point your first finger in the direction of the magnetic field from north to south now point your second finger in the direction of the conventional current in other words positive to negative finally the direction that your thumb is pointing shows you the direction of the motion in other words the force so I'd like to use Fleming's left hand rule to show that the direction of motion of this wire will be upwards pause the video now and try this yourself okay this shows a simple version of Fleming's left hand rule and we can see that the thumb points up in this case shown that the motion is upward now there's one final point about the mortu effect if the conductor is parallel to the magnetic field then it will not experience a force so this shows the conductor running parallel to the magnetic field and this conductor will not experience a force whereas this conductor is at right angles to the magnetic field so this will experience a force remember your fun plenty of questions on the motor effect and my vision workbook and you can get that by clicking on the link above [Music]