Torque on a Dipole. An electric dipole with dipole moment p is in a uniform external electric field E. (c) Show that for the stable orientation in part (b), the dipole's own electric field tends to oppose the external field.

Video transcript

Hey, everyone in this problem, we're told that an electric die pool is an assembly of two equal opposite charges separated by a distance D when placed in an electric field, the dye poll has one stable orientation and the torque on that die pole for the orientation is zero were asked, does the disciples electric field point in the same direction as the external electric field or oppose it? Alright. So let's start writing out by some of this information we're given in the problem. So we're given information about the torque and recall that the torque is equal to the electric dipole moment crossed with the external electric field. Okay. And we're told in the problem that this is equal to zero. Now, if we have two vectors, the cross product of two vectors equal to zero, this tells us that those two vectors. So the electric dipole moment and the external electric field, okay or either parallel or anti parallel. Okay. All right. So we know now that they're either parallel or anti parallel. That makes sense because we're being asked if they're in the same direction or the opposite direction. Alright. Now we're told that we have a stable orientation in the stable orientation. The angle between P and the external Electric Field by is equal to zero. Okay. And the two vectors P N E are parallel. So what this means is that our electric dipole moment and our external electric field pointing the same direction. Alright. That's a good start. But we're trying to figure out whether the dye pulls electric field points in the same direction as the external electric field. Alright, well, the electric dipole moment P is going to point from negative two positive. He always points in that direction which tells us that the external electric field since we found that these are parallel is also going to point from negative positive. All right. So we have a concrete direction on our external electric field. What about our diet? Well, we know that the electric field due to a die pool always points from positive two negative. So we have the external electric field pointing from negative to positive. We have the dye pole electric field pointing from positive to negative. And so the Disciples electric field is opposing the external electric field. Okay. They're acting in the opposite direction. We look at our answer traces and we see that we have answer choice B the Disciples electric field points in the opposite direction as the external electric field. That's it for this one. Thanks everyone for watching. See you in the next video.