Lec4 - Physics 8B Professor Catherine Bordel 09/03/10...

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Physics 8B Professor Catherine Bordel 09/03/10 Lecture 4 ASUC Lecture Notes Online is the only authorized note-taking service at UC Berkeley. Do not share, copy, or illegally distribute (electronically or otherwise) these notes. Our student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. D O N O T C O P Y Sharing or copying these notes is illegal and could end note taking for this course. ANNOUNCEMENTS Some students asked if the deadline for homework could be postponed to Friday at midnight instead of 8 pm. Who would like to switch from 8 pm to midnight? Student : How about Saturday midnight? Alright, if the other section agrees. It’s not a problem for me. We just need to make sure it’s going to be the same deadline for the two sections so we try to post the homework at the same time. If we can manage to have the agreement from the other section, then that’s okay. Student : When will you be posting homework? Usually Friday evening, I’ll post it for the next week. LECTURE We’re going to start with the demo. We have here two spheres with a conducting surface. On top of one of them we can place other plates and rice pops. The basic principle is the same as the electroscope, where we have a free arm, so when you build up some charge, the repulsion between the free arm and the other arm causes the free arm to move. We use power to move a belt that creates friction that builds up charge on the sphere, and then you’ll see what happens to the things we put stuff on top of one sphere. Demo: Stacks pie pans on top of one of the spheres. Turns on machine, one by one the pans fly off the top of the sphere. Places rice pops on top of the sphere, they fly off one by one. This is just an illustration of what you’ve seen already with the electroscope. The two objects touching each other experience repulsion so the things on top of the sphere move in the opposite direction. We’re going to talk about field lines. I want to give you three main characteristics of electric field lines. Fields apply to many parts of physics, it’s just a quantity you can map out. The electric field is created by a point charge or a sphere full of charge, for example, and everywhere in space you have an electric field. We can measure these lines using an
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This note was uploaded on 10/02/2010 for the course PHYSICS 8B taught by Professor Shapiro during the Spring '07 term at University of California, Berkeley.

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Lec4 - Physics 8B Professor Catherine Bordel 09/03/10...

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