2. 22-1 Electromagnetism The new science of electromagnetism(the combination Of electrical and magnetic phenomena) was developed. 22 Electric Charge

3. 1 Electric Charge is an intrinsic characteristic of the fundamental particles making up those objects. 2 Two kinds of charge: positive charge and negative charge. The object contains equal amounts of these two kinds of charge is said to be electrically neutral. 22-2 Electric Charge

4. Charge with the same electrical sign repel each other, and charges with opposite electrical signs attract each other.

5. Such as metals,tap water,and human body,some of the negative charge can move rather freely. Conductors: Insulators: Such as glass,chemically pure water,and plastic,none of the charge can move freely. 22-3 Conductors and Insulators

6. Semiconductor: Such as silicon and germanium,are material that are intermediate between conductors and Insulators. Superconductors: They present no resistance to the movement of electric charge through them.

7. atom nucleus negative charge electrons positively charge proton electrically neutral neutron The properties of conductors and insulates are due to the structure and electrical nature atoms.

8. CHECKPOINT

9. How can we know the electrostatic force between small electric charge q 1 and q 2 at rest and separated by a distance r at this 3 situations? 22-4 Coulomb’s Law

10. K is a constant.For practical reasons,the SI unit of charge is derived from the SI unit of electric current,the ampere(A).

11. The SI unit of charge is the coulomb (C). It is defined in terms of the unit of the unit of current,the ampere (A),as the charge passing a particular point in 1 second when there is a current of 1 ampere at that point. The Coulomb and Ampere

12. For historical reasons (and because doing so simplifies many other formulas),the electrostatic constant k of Eq.22-1 is usually written 1/4πε 0.The Coulomb’s law becomes

13. Coulomb’s law describes the electrostatic force between small (point) electric charge q 1 and q 2 at rest (or nearly at rest) and separated by a distance r Here:ε 0 =8.85×10 － 12 C 2 /Nm 2 1/4 πε 0 =k=8.99×10 9 Nm 2 /C 2

14. The force of attraction or repulsion between point charges at rest acts along the line joining the two charges. How about the situation if there are more then two charges are present?

15. A shell of uniform charge attracts or repels a repels a charged particle that is outside the shell as if all the shell’s charge were concentrated at its center. The two shell theorems for electrostatics are:

16. If a charged particle is located inside a shell of uniform charge, there is no net electrostatic force on the particle from the shell.

17. Sample Problem 22-1

18. (a) Step one: Step two:

19. (b) Step one: Step two:

20. 9.00×10 － 25 and 0 0 Second key idea

21. (c)

22. Method 1 Step one: Step two: Step three:

23. Method 2 Step one: Step two:

24. Step three: Step four:

25. “electrical fluid” is also not continuous but is made up of multiples of a certain elementary charge. Any positive or negative charge q that can be detected can be written as and the elementary charge has the value: q=n e, n=±1,±2,±3,…, e=1.60×10 -19 C. 22-5 Charge Is Quantized

26. ParticleSymbolCharge Electron e or e - -e Proton P +e Neutron n 0 When a physical quantity such as charge can have only discrete values rather then any value, we say that the quantity is quantized.

27. Sample Problem 22-4 (a)

28. (b)

29. Initially sphere A has a charge of –50e and sphere B has a charge of +20e.The spheres are made of conducting and are identical in size. If the spheres then touch,what is the resulting charge on sphere A? Question

30. This hypothesis of conservation of charge has stood up under close examination, both for large-scale charge bodies and for atoms, nuclei, and elementary particles. 22-6 Charge is conserved