TPR Cracking 2 PS Q5: Why is there no net force

[bear2roo]

I attached the problem + answer. I got it right with some "intuition-guessing" but I really can't seem to reason out why.

First, how do we know that this molecule is neutral?
Second, why is there no net force between the capacitor plates? Is that a content thing I forgot? E&M is an iffy subject for me.

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[sps27]

I attached the problem + answer. I got it right with some "intuition-guessing" but I really can't seem to reason out why.

First, how do we know that this molecule is neutral?
Second, why is there no net force between the capacitor plates? Is that a content thing I forgot? E&M is an iffy subject for me.

So when there is no current flowing, the plates are uncharged. When the connection is closed, charge starts to build up, +ve on one plate and -ve on the other plate. When we have a molecule with a dipole, it means that one end of the molecule has a +ve charge and other end of the molecule has a -ve charge separated with some distance between them, hence a dipole. If we place this between the plates, (at a 45 deg angle) the +ve charge will get attracted to the -ve plate and -ve charge to the +ve plate. These two forces cancel out vectorially so there is no net resultant force. That being said, there is a net torque or a couple in this case, why, because the two charges in the dipole are at a distance from one another and their line of action is perpendicular to the dipole axis.

If the dipole was placed perpendicular to the plates with +ve charge towards -ve plate and -ve charge towards +ve plate, there will be no charge and no torque, why, because the line of action of the two forces will be along the dipole axis. Because it is placed at an angle, 45 deg or anything else, it will experience a torque or a couple to be more precise.

I hope that makes sense.