‫Welcome back, I hope you tried this fun exercise yourself.
‫Let's look at it now.
‫First of all, what direction will the cross be give you?
‫According to the right hand rule, the Krosby will give you an upward direction.
‫Your fingers first go in the direction and then they go in the B direction into the screen.
‫And that's why you don't see the fingers, because they go into the screen.
‫These are knuckles here, so your thumb goes up.
‫So you might think that the force goes up and therefore the electron as well.
‫So you might think that the electron will go in this direction, that it will go upwards.
‫Now, that would be true for a proton that has a positive charge, right?
‫A positive cue.
‫However, you have an electron and an electron has a negative charge and negative.
‫Q So you will have an upward direction produced by this operation here.
‫However, since your cue is negative, then your direction will be reversed like this.
‫So since you have a force now that is in the downward direction, then the electron will actually start
‫moving down as well.
‫But it also has this forward velocity.
‫So after some time it will end up here.
‫But then you have a new velocity vector, which is in this direction like this, and now this formula
‫will give you a force in this direction.
‫First, your force was in this direction and now it's in this direction because your velocity vector
‫is in this direction.
‫And then again, you're here, your velocity is in this direction and your force is in this direction.
‫And you see where it is going.
‫Right.
‫You can see that the force vector is a centripetal force that will make the electron move in a circle
‫like this.
‫OK, this doesn't look like a perfect circle, but actually it would be a perfect circle because what
‫happens here happens on a continuous basis.
‫Every infinitesimal second, the velocity vector of the particle changes and therefore the force vector
‫changes its direction as well.
‫So if that thing happens on a continuous basis, then in the end you see that you force vector is a
‫centripetal force in your electron will move in a perfect circle.
‫And unless the conditions change, for example, maybe you have a different velocity vector or a different
‫magnetic field vector.
‫Unless those conditions change, the electron will stay here and make this circle forever.
‫That's how scientists control charged particles.
‫They do it with magnetic fields.
‫So there you go.
‫Now you know the dot and cross products and some of their applications.
‫In the next video, we will look at mass moment of inertia and inertia tensor.
‫So thank you very much and I'll see you in the next video.