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# In the Millikan oil-drop experiment illustrated in Figure 15.21 an atomizer (a sprayer with a fine nozale) is used to introduc many tiny droplets of oil between two oppositely charged parallel metal plates. Some of the droplets pick up one or more excess electrons. The charge on the plates is adjusted so that the electric force on the excess electrons exactly balances the weight of the droplet. The idea is to look for a droplet that has the smallest electric force and assume it has only one excess electron. This strategy lets the observer measure the charge on the electron. Suppose we are using an electric field of $3 \times 10^{4} \mathrm{N} / \mathrm{C}$ . The charge on onc clectron is about $1.6 \times 10^{-19}$C. Estimate the radius of an oil drop of density 858 $\mathrm{kg} / \mathrm{m}^{3}$ for which its weight could be balanced by the clectric force of this field on one clectron. (Problem 42 is courtesy of E. F. Redish. For more problems of this type, visit www. physics.umd edu/perg/.)

## 0.52$\mu \mathrm{m}$

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### Video Transcript

Hello, Strengths. Let's start or discussion. Millikan, Drop experiment. Americans drop experiment. Okay. Suppose you have to metal players off a poser. Charges I draw off electrons is exactly balanced by its weight. It's means that if this is a draw, then a downward force I'm she will acting here. Okay. And two balances downward. Fourth, there should be an electrostatic force is applying on this part. A language. Ah, for direction. It means that this is a port city. Went This is the negative plate. Okay, Now we have to find out that video's off this drone, which is filled with electrons. Okay, so firstly, this'll drove I m g s banished by electrostatic force curie. So from here, mass will come. So, Toby, you eat by muscle drop will be doing by G. Okay, now the dance city or brought really mass by volume and from hair volume comes out to be must buy density and volume over drop is because it's very kinship. Fall upon three ir que mass weight density. So from here, value off our Q will comes. Toby must buy density three up on full by. Okay, So if we put the values off mask. That is this cube i g. So it will be three upon for by you even by G and one upon density and gilded route. So by this formula, we will get the Nadya's off this drug. No charge on electrons are 1.6 inter tenderness. Par minus 19. Coolum. Okay. Electric field that is applied here is three entertained this part for you to Bakula and the density off the drop is 8 58 k g four meter cubed bip and value of G s. 9.8. Meet up a second square. So five putting all the values here. We will get a radius off Jiro point Geo 0.5 to interrupt. Endless bomb minus six meter. It means that we will get rid our radius. All Jiro, point five to my group meter. This is the radius off drop in our Milken's experiment. Well, this is all from me for test video. I hope you will like the video. Thank you.

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