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2007 Nobel Prize in Physics: Albert Fert (R) and Peter Grunberg

Invention of the first Transistor in Nov.17-Dec.23 1947, the most important invention of the 20 th century. 2007 Nobel Prize in Physics: Albert Fert (R) and Peter Grunberg. Giant Magnetoresistance. Goals. Some knowledge of physics

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2007 Nobel Prize in Physics: Albert Fert (R) and Peter Grunberg

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

  2. 2007 Nobel Prize in Physics:Albert Fert (R) and Peter Grunberg Giant Magnetoresistance

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

  4. 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

  5. Chapter 15 Electric Forces Electric Fields

  6. Outline for Today • Electric Charge • Coulomb’s Law

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

  8. 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

  9. 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

  10. 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

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

  12. Question: A negative electric charge • interacts only with positive charges • interacts only with negative charges • interacts with both positive and negative charges • may interact with either positive and negative charges, depending on circumstances Answer: c

  13. Question: An object has a positive electric charge whenever • it has an excess of electrons • it has a deficiency of electrons • the nuclei of its atoms are positively charged • the electrons of its atoms are positively charged Answer: b

  14. 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

  15. Metal: dr/dT>0

  16. 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

  17. Insulator: dr/dT<0

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

  19. Polarization

  20. Charging by Rubbing

  21. Charging by Induction

  22. +q +q F F 2 1 21 12 q q r F 1 2 ke = 12 12 r 2 12 Coulomb’s Law

  23. Coulomb’s Law, cont. • ke is called the Coulomb Constant • ke = 8.99 x 109 N m2/C2 • Typical charges can be in the µC range • Remember, Coulombs must be used in the equation • Remember that force is a vector quantity

  24. m Q Q m F F 1 1 2 2 G ke = = 12 12 r r 2 2 12 12 Coulomb forceGravitational 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

  25. 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 Fe=kQeQp/r2=(9.0x109 N•m/C2)(1.6x10-19 C2)/(5.3x10-11 m)2 =8.2x10-8 N Fg=Gmemp/r2 =(6.7x10-11 N•m/kg2)(9.11x10-31 kg)(1.67x10-27 kg)/(5.3x10-11 m)2 =3.7x10-47 N me=9.11x10-31 kg, mp=1.673x10-27 kg The electric force is over 1039times greater than the gravitational force

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