1. Invention of the first Transistor in Nov.17-Dec.23 1947, the most important invention of the 20 th century

3. 2007 Nobel Prize in Physics: Albert Fert (R) and Peter Grunberg Giant Magnetoresistance

4. Goals Some knowledge of physics Critical thinking, idealization, approximation, mathematical and graphical representations of phenomena.

5. Physics 213 Electric Charge, Electric Fields, Electric Forces, Electric Energy, Electric Currents Magnetism Electromagnetism Light and Optics Modern Physics including Special Relativity, Quantum Mechanics and Nuclear Physics

6. Chapter 15 Electric Forces Electric Fields

7. Electric Charge Coulomb’s Law Outline for Today

8. What is electric charge? Like rest mass, it is a fundamental property of some of the elementary particles of which all matter is composed Electric charge is the fourth quantity we have learned (energy, linear momentum, and angular momentum)

9. Properties of Electric Charges Two types of charges exist –They are called positive and negative –Named by Benjamin Franklin Like charges repel and unlike charges attract one another Nature’s basic carrier of positive charge is the proton –Protons do not move from one material to another because they are held firmly in the nucleus

10. More Properties of Charge Nature’s basic carrier of negative charge is the electron –Gaining or losing electrons is how an object becomes charged Electric charge is always conserved –Charge is not created, only exchanged –Objects become charged because negative charge is transferred from one object to another

11. Properties of Charge Charge is quantized –All charge is a multiple of a fundamental unit of charge, symbolized by e –Electrons have a charge of –e –Protons have a charge of +e –The SI unit of charge is the Coulomb (C) e = 1.6 x 10 -19 C

12. Question Question: Electric charge (a)is a continuous quantity that can be subdivided indefinitely (b)is a continuous quantity but it cannot be subdivided into smaller parcels than 1.6x10 -19 C (c)occurs only in separate parcels, each of 1.6x10 -19 C (d)occurs only in separate parcels, each of 1 C Answer: c

13. Question: A negative electric charge (a)interacts only with positive charges (b)interacts only with negative charges (c)interacts with both positive and negative charges (d)may interact with either positive and negative charges, depending on circumstances Answer: c

14. Question: An object has a positive electric charge whenever (a)it has an excess of electrons (b)it has a deficiency of electrons (c)the nuclei of its atoms are positively charged (d)the electrons of its atoms are positively charged Answer: b

15. Conductors Conductors are materials in which the electric charges move freely –Copper, aluminum and silver are good conductors –When a conductor is charged in a small region, the charge readily distributes itself over the entire surface of the material

16. Metal: d  /dT>0

17. Insulators Insulators are materials in which electric charges do not move freely –Glass and rubber are examples of insulators –When insulators are charged by rubbing, only the rubbed area becomes charged There is no tendency for the charge to move into other regions of the material

18. Insulator: d  /dT<0

19. Semiconductors The characteristics of semiconductors are between those of insulators and conductors Silicon and germanium are examples of semiconductors

20. Polarization

21. Charging by Rubbing

22. Charging by Induction

23. Coulomb’s Law r 1 2 F q = keke 2 q 12 21 +q+q +q F 12 F 21 r 12

24. Coulomb’s Law, cont. k e is called the Coulomb Constant –k e = 8.99 x 10 9 N m 2 /C 2 Typical charges can be in the µC range –Remember, Coulombs must be used in the equation Remember that force is a vector quantity

26. Coulomb force Gravitational force But electric forces may be either attractive or repulsive, whereas gravitational forces are always attractive. That is why matter in the universe tends to come together to form large bodies, these bodies are always found in groups, such as galaxies of stars and families of planets. On an atomic scale, electricity is much more important than gravity r 1 2 F m = G 2 m 12 r 1 2 F Q = keke 2 Q

27. Example: The hydrogen atom has the simplest structure of all atom, consisting of a proton and an electron whose average separation is 5.3x10 -11 m. The mass of electron and proton is 9.1x10 -31 kg, 1.67x10 -27 kg, respectively F e =kQ e Q p /r 2 =(9.0x10 9 Nm/C 2 )(1.6x10 -19 C 2 )/(5.3x10 -11 m) 2 = 8.2x10 -8 N F g =Gm e m p /r 2 =(6.7x10 -11 Nm/kg 2 )(9.11x10 -31 kg)(1.67x10 -27 kg)/(5.3x10 -11 m) 2 = 3.7x10 -47 N m e =9.11x10 -31 kg, m p =1.673x10 -27 kg 10 39 The electric force is over 10 39 times greater than the gravitational force