1. Describe what happens, on a microscopic level, when an...

1. Describe what happens, on a microscopic level, when an object is charged by rubbing. For instance, what happens when a plastic pipe is rubbed with a cloth? 2. Two pith balls hang side by side close to each other without touching as shown in the figure below. They are both neutral to begin with. a. A plastic rod is rubbed with wool. Describe as negative, positive or neutral the total (net) charge of a system consisting of the rod and the cloth. Explain your reasoning. b. A student touches sphere A briefly with the rod and then removes it. What is the charge state of A? Same as the rod or opposite charge of the rod? c. Then he brings the rod close to sphere A but does not touch it. What will happen to A? Explain your reasoning. d. Now sphere B is brought very close to A but does not touch it. What will happen to the spheres? Explain your reasoning.

Transcript

00:01 Okay, so we've got several parts here.

00:02 For number one, what happens when you charge by friction? they're saying here by rubbing.

00:07 So when you charge by friction, you've got two surfaces that are in contact with each other.

00:13 I'm just going to draw a couple positive and negative charges in here.

00:18 There would be many more than just the ones i've drawn.

00:21 And two materials rub together.

00:22 Now, it depends on what the materials are made of, but one material is going to gain electrons, the other is going to lose.

00:28 So if i draw this again, let's just say that the object on the left is going to be the one that loses electrons, and the one on the right is going to be the one that gains.

00:39 Okay, so one, two, three, four.

00:42 So now we're going to have a positive charge on the left and a negative charge on the right.

00:47 So the best way to say this would be electrons are transferred from one to the other.

00:57 Okay, but there's a little diagram of it.

00:59 For number two, we've got two pitfalls that are hanging here.

01:02 They're both neutral.

01:05 Okay, and for part a, it says, you know, plastic rod is rubbed with wool.

01:14 What is the total charge here, positive, negative, or neutral? so we don't know which object is going to gain or lose electrons.

01:22 It's going to be very similar to this picture i just drew.

01:25 One of them is going to gain electrons, the other is going to lose.

01:27 The total charge, though, is going to be neutral because notice how we've got four positives and four negatives.

01:32 They're not evenly dispersed, but the total charge should be zero.

01:36 That's called conservation of charge.

01:38 So the net charge is zero or neutral.

01:51 Okay, and we want to explain our reasoning here.

01:56 So we'll say one object gains electrons, the other loses.

02:17 Okay, and they would gain and lose equal amounts.

02:21 Okay, for part b here, student touches sphere a briefly, and then with the rod and then removes it, what is the charged state of a? same as the rod or opposite of the rod.

02:33 So let's just say that the rod is negatively charged.

02:37 We know the rod is charged.

02:38 We're not sure what it's charge is.

02:39 Let's say it has a negative charge.

02:41 If it touches another neutral object, okay, so i'll draw this like that...

Question

Please give Ace some feedback