09_coulomb

# 09_coulomb - Lesson 9 Coulomb's Law Charles Augustin de Coulomb Illustration 1 Charles Coulomb Before getting into all the hardcore physics that

This preview shows pages 1–3. Sign up to view the full content.

Lesson 9: Coulomb's Law Charles Augustin de Coulomb Before getting into all the hardcore physics that surrounds him, it’s a good idea to understand a little about Coulomb. He was born in 1736 in Angoulême, France. He received the majority of his higher education at the Ecole du Genie at Mezieres (a french military university with a very high reputation, similar to universities like Oxford, Harvard, etc.) from which he graduated in 1761. He then spent some time serving as a military engineer in the West Indies and other French outposts, until 1781 when he was permanently stationed in Paris and was able to devote more time to scientific research. Between 1785-91 he published seven memoirs (papers) on physics. One of them, published in 1785, discussed the inverse square law of forces between two charged particles. This just means that as you move charges apart, the force between them starts to decrease faster and faster (exponentially). In a later memoir he showed that the force is also proportional to the product of the charges, a relationship now called “ Coulomb’s Law ”. For his work, the unit of electrical charge is named after him. This is interesting in that Coulomb was one of the first people to help create the metric system. He died in 1806. The Torsion Balance When Coulomb was doing his original experiments he decided to use a torsion balance to measure the forces between charges. You already learned about a torsion balance in Physics 20 when you discussed Henry Cavendish’s experiment to measure the value of “G” , the universal gravitational constant. Review Cavendish’s work in the Physics 20 notes (Chapter 4 Lesson 29: Newton's Law of Universal Law of Gravitation) if you need to. Coulomb was actually doing his experiments about 10 years before Cavendish. He set up his apparatus as shown in Illustration 2 with all spheres charged to have the same sign. He charged one of the free moving spheres by touching it to an already charged object (charging by conduction). He then touched that one sphere to the other free moving sphere (charging it by conduction). Each of the free moving spheres was then touched to one of the spheres on the rod (guess what. .. charging by conduction!). 9/28/2011 © studyphysics.ca Page 1 of 7 / Section 10.2 Illustration 1: Charles Coulomb Illustration 2: The Torsion Balance

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Although he didn't know the actual charge on any particular sphere, Coulomb did know that each sphere had an equal charge to all the rest. Coulomb also altered the experiment by using spheres of different sizes so he could get the amounts of charge in different ratios, and by touching spheres to other objects to get other ratios of charges. Because like charges repel, the spheres on the rod twist away from the other spheres.
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

### Page1 / 7

09_coulomb - Lesson 9 Coulomb's Law Charles Augustin de Coulomb Illustration 1 Charles Coulomb Before getting into all the hardcore physics that

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online