0:00
All righty.
00:01
So we've got a magnetic field problem here.
00:05
I'm just going to write down this lorentz force equation, which we've been using quite a bit here.
00:15
All right.
00:17
This problem's a little bit different.
00:19
We'll see what i mean here.
00:20
So i'll just, i'm going to dive right in.
00:22
Part a to give us some information.
00:25
The first thing they give us is they give us direction of our positively charged particle.
00:30
I'm not going to bother writing a positive with a circle around it there.
00:33
We'll just, we know for every situation given in this problem, we're all positive.
00:38
We also know the direction of the resultant force, not the magnetic field.
00:46
We don't know this.
00:47
Don't know that guy, unfortunately.
00:49
We just know this guy.
00:51
I'll sketch that out so you get an idea where it's at.
00:54
It's pointing upward.
00:58
All right.
00:58
This is our f sub b.
01:03
This guy down here is our velocity vector.
01:07
Okay.
01:07
Our job, figure out which direction b is pointing in.
01:12
We don't know.
01:14
So the way i do this is we're given v, which no matter what we do, if we're trying to figure out, say, you're trying to figure out your magnetic field force vector, this guy right here.
01:26
You know, it always starts the same way.
01:28
You find, you use the right hand rule, and you stick up your right hand, and you point your fingers in the direction of the velocity vector.
01:35
So that's a great starting point here.
01:37
Take your right hand, stick it up in the air, and i'm pointing it in the direction of the velocity vector.
01:44
Right? now, normally i curl my fingers at this point in the direction of the magnetic field, but i can't do that because i don't have a magnetic field here.
01:57
But what i do is i kind of use almost a guess and check method.
01:59
All right.
02:00
So fingers are right now pointing toward the velocity vector all to the right.
02:05
And now i'm just testing stuff out.
02:06
Say i curl my fingers or say i curl my fingers downward, hypothetically.
02:12
Now my thumb's going into the page.
02:13
Well, that can't be right.
02:14
Okay, let's try a different one here.
02:16
Velocity vector pointing to the right.
02:18
My fingers are pointing the right what if i curl my fingers into the page okay well now my thumb is pointing up and that's good because that is the direction where this guy is pointing so excellent i have found the correct answer here the magnetic field is pointing into the page and i recommend after you do this do one more test real quick let's test it out i'm holding my hand my right hand up pointing my fingers to the right of the page now i'm orienting my hand so that i can curl my fingers in the direction of that magnetic field, which is into the page.
02:56
And when i'm doing that, my thumb is pointing upward in alignment with our resultant force vector.
03:04
Excellent.
03:05
That means this is good to go.
03:06
You can give it a little check.
03:07
Keep moving.
03:07
All right.
03:08
So part b.
03:10
We'll do that right here.
03:12
In this situation, we've got a velocity vector.
03:16
And just to be clear, i was in my last part there.
03:19
Let's use my colors here...