The conducting rod ab shown in Fig. E29.29 makes contact with metal rails ca and db. The apparatus is in a uniform magnetic field of 0.800 T, perpendicular to the plane of the figure.

(b) In what direction does the current flow in the rod?

Video transcript

Hi everyone today, we are going to find direction of current flowing in the conductor where in this figure itself, it has showed that a conductor PQ is in contact with metal rails, M. P. And N. Q. With a uniform magnetic field of 0.65 tesla around it. So the magnetic field itself is perpendicular to the plane of the figure, which means that the magnetic field is either going outside of the paper plane or inside of the paper plane. So in this case we know that it is going inside because of the process indicating here. So we know that the B. Here is actually going towards the plane of the page. Next we want to identify that the conductor B. Q. Here is moving towards Mn closing this, making this loop smaller and smaller. So we know that first the B is flowing directed into the page and because the B. Q conductor is uh going closer and closer to Mn, the flux actually decreases as the PQ is getting closer and closer to Mn. So I'm just going to write that down as P. Q gets closer to mm. Then the flux, the magnetic flux actually decreases and because of that than the magnetic field itself also decreases. Then to counter that, then what we want to do is to make sure that we create an induced current that will actually put the system at a balance again. So, because the magnetic field itself actually decreases, we want to make the induced current to actually be along the direction of the magnetic field itself. We know that the magnetic field is going into the page. So we want the induced magnetic field from the current two also be going into the pitch to also be going into the pitch essentially to put the system back to equilibrium. Okay, so the flux decreases as the bar moves off word. So the magnetic field of the induced current that we need to make things go back to equilibrium should be directed into the page, should be directed into the page. This is just to strengthen the decreasing flux. Okay, so to produce the induced magnetic field in this direction there, then we will have to actually use the right hand rule to determine the direction of the current that we wanted to be going into. Okay, so looking at this loop right here, we can use our right hand rule where our four fingers is gonna be the direction of the end of the current. While the tom is going to be the direction of our induced magnetic field. So when we have this current going clockwise, just like, so then we know that our finger or four fingers will be going clockwise and therefore our thumb will be pointing into the plane of the page. So that is definitely what we wanted in this particular example. So when the actual current itself is going clockwise, then we know that it is going from P to Q, which is the answer. B two Q. Which is the answer to this problem. So it is going to be option B, just like so, so this is a very conceptual practice problem. If you guys need more lessons videos, make sure to check out our other lesson videos on this to gain a better understanding of this, but that will be all for this particular problem. Thank you.