17.1 Cloud and Bubble Chamber

Okay, in this lesson, we're going to start looking at our last chapter for the course. We're going to explore what iCloud and bubble chamber is, and what it does. The idea, up until now, is that we've identified electrons and their charge, as well as protons, neutrons, and all these different particles within an atom. The question is, how do we know what they should do in a magnetic field and an electric field? And furthermore, how do we actually see that it does that? How do we prove that it's true? This is where the cloud and bubble chambers come in. The concept is, how can we reach around in the dark? Or, how can we find and see these things in areas that we can't actually see? Physicists got the idea from Clara Farrell's Wilson, who was using cloud chambers to try to mimic... What happens in clouds in terms of weather patterns? Well, basically, if you were to make a mini cloud in a glass chamber, you would realize that if there were charged particles in there, they would interact with some of the water vapor. As a result, you would see these little vapor trails behind the particles, similar to when you see an airplane pass through the sky. So, physicists decided to replicate this idea. They created a cloud chamber, where they would move a charged particle through it and observe the trail left behind. A bubble chamber, on the other hand, is pretty much the opposite. Instead of having water vapor inside that we try to disturb or change, the idea is to put in a super-saturated liquid. Next, we introduce some sort of gas that is already at boiling point, ready for this liquid to boil. Not quite. Then, we shoot a charged particle into the liquid, and the friction that it causes as it goes through it actually boils the particles that it touches. It basically leaves a little bubble chamber. So, they both kind of do the same thing. One sort of leaves this little trail of kind of in the clouds. The other one basically leaves a trail of bubbles. The idea behind both of them, though, is that we can actually see what's going on. You can see in this diagram at the top, a charged particle was actually shot in, and you can see it sort of makes a curve and leaves a little trail of bubbles behind. Because we know which direction magnetic fields are in and things like that, we can then figure out which direction things are curving due to the magnetic force, what the radius is, what the speeds would be, charge-to-mass ratio, and we can also see which way they would actually spin. So, in terms of things orbiting, they actually spin as they go. In this, we can kind of measure that as well. The biggest drawback from both cloud and bubble chambers is that it's pretty tough to detect a neutral particle. So, if you have something neutral, they see they're just going to go straight through, which is pretty tough to see. So, in terms of a cloud chamber, you wouldn't be able to see neutrons. In terms of a bubble chamber, the friction and the energy that it passes would still leave a little bit of bubbles behind, which is typically why we use bubble chambers more universally. So, the best way to get these things to work basically is to put the chambers in a magnetic field, and then we just basically allow these things to curl. So we have F[sub]M[/sub] = F[sub]C[/sub]. If we look at this first example, we know our magnetic force is Q [symbol]v[/symbol] [symbol]v[/symbol]. We know our circular force is M [symbol]v[/symbol][sup]2[/sup] / R, and we can actually figure out charge to mass particles, if we go from charged to mass, that is the over BR. So for this question, they give us the velocity of the particle, stating that it is moving at 0.2024 times 3 times 10 to the 8th power. They also provide RB in the question as 4.75 times 10 to the negative 3rd power and the radius as 8 times 10 to the negative 3rd power. By doing the calculations, we can see that the charge-to-mass ratio is 1.77 times 10 to the negative 11th power. When comparing this to [Music] Electron: So, if we do charge the mass, we just use the basic charge, elementary charge (1.6 * 10^-19), and divide that by the mass of the electron. When we do that calculation, we see that we get pretty much the same answer. The first one is 1.77, and this one works out to about 1.76. But we see that we get pretty much the exact same thing. So when you do these, oh, three was positive. I'm not making all of them for both, but we can see that the Petrarca mass ratio works out to be the same. So based on just a simple example like this, we can see, okay, well, we know these particles are curving, they're going in opposite directions, and it works out that the charged particles have pretty much the same charge to mass ratio of an electron. So, if these two things were shot in from the left, we then know that one has to be positive and one has to be negative. Therefore, we know one is an electron and one is a positron. Additionally, if we know that the magnetic field is coming out of the page, we can use our third left-hand rule. If we put our thumb to the right, point our magnetic field over the page, we can see that the force would go upwards. So, for our left hand, our force goes upwards, indicating that the upper one is the electron. On the other hand, for our right hand, the force goes downwards, indicating that the lower one is the positron. And that's it. You can see the idea with bubble chambers and cloud chambers. The idea is to, first of all, see the particles as they react in the magnetic field. Then, we can use things like the size of the array, the ratio of the curves, and the direction they're going to determine whether they're positive or negative, and whether they're larger particles. So, for example, if we were to suppose the same diagram and shoot a positive particle, like a proton, we know that it's going to curve downwards. However, because the proton has a larger mass, the radius would also be much larger. So, we would see it curve in a wider spiral shape, not just a tight spiral. The radius would end up being much larger, and that's all.