A negative charge in a spectrometer is accelerated in the negative x-axis. It is later deflected and collides some distance ABOVE velocity selector. What are the orientations of the electric and magnetic fields, respectively, inside the selector?

Hey guys, let me try this practice problem. So here we're looking for the direction of the electric field and the magnetic field in a mass spectrometer. Let's check it out. So we have a negative charge, negative q. So you gotta be careful, this means you're gonna use a left hand rule. It's moving being accelerated in the negative x axis, which is to the left. So I'm actually gonna start this over here and draw some parts of this thing. It's gonna be accelerated this way. It's going to be deflected and is going to collide above the velocity selector. Remember at some point it runs through a velocity selector, the right charges, the target charges will make it all the way through straight and then they will be deflected over here. This one it says is hitting up here somewhere above, that's the keyword, velocity selector, which means it's gonna do this. K. And we wanna know what is velocity selector, which means it's gonna do this. Okay. And we want to know what is the direction of the electric field and magnetic field. Remember there's there's an electric field only here but there's a magnetic field here and here as well in the deflection zone. Okay, and we wanna know these directions. So where do you start? Well, it depends on how much information you have. The electric field only exists here. The only way you can know the electric field is somehow if you know the direction of the electric force. Okay? Can you know the direction of the electric force? Well, for that, the only way to know that is by actually looking here and this path here is telling you that the magnetic force has to be going up that causes this thing to deflect, right, and then as you move you go like this which means that in the middle here, the magnetic field is also up. Okay? The magnetic force is up. I'm sorry. Which means the electric force must be down. Okay? So the magnetic force is up which means that here it has to be down. Now if you remember, if you are a positive charge, you go in the direction of the fields. If you're negative charge, you are going against the fields. So if the electric force is down but your negative charge, this means that the electric field is actually up. Okay? So the electric field is up. Now we know that it's at either a or b. Alright. Now what about the direction of the magnetic field? For that, we're gonna use the right hand rule. Actually, I'm sorry, we're gonna use the left hand rule because this is a negative charge. So we want our force to be up so something like this, right? Because we're gonna be curving like this, we want our force to be up. Now the problem velocity is instead. Force FB is still up. The velocity is this way and notice my fingers are going away from me which means they're going into the page. So the answer is up and into the page. And into the page is a little x which means the magnetic field here are x's and here are x's as well. Cool. That's it for this one. Super important that you know these directions. Let's keep going.

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A negative charge in a spectrometer is accelerated in the negative x-axis. It is later deflected and collides some distance ABOVE velocity selector. What are the orientations of the electric and magnetic fields, respectively, inside the selector?

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