Electricity. Greeks learned about charge by rubbing amber (fossilized tree resin) Greek word for amber = elektron. Picture from wikipedia

Transcription

1 Electricity Greeks learned about charge by rubbing amber (fossilized tree resin) Greek word for amber = elektron Picture from wikipedia

2 Atomic Structure - A Who s Who J. J. Thomson Ernest Rutherford Robert Millikan Discovered electron (Measured charge divided by mass) Discovered nuclear structure Measured charge of electron (thereby finding its mass)

3 Who s Who in Electricity Benjamin Franklin Charles-Augustin de Coulomb Henry Cavendish Discovered electric force law Defined positive vs. negative charge

4 Who s Who in Electricity Michael Faraday Left school at age 13 became book binder read books he bound learned science (but not math!) asked author he read to work in his lab became great scientist and inventor invented notion of fields

5 Who s Who in Electricity Karl Gauss Numerous contributions to electromagnetic theory

6 Who s Who in Electricity Alessandro Volta Invented battery

7 Who s Who in Electricity Otto von Guericke Credited with first electrostatic generator - Put ball (made of sulphur) on wooden cradle, spin it and rub by hand

8 Who s Who in Electricity Ewald Jürgen von Kleist Pieter van Musschenbroek Independently developed the Leyden jar, an early capacitor (1745)

9 Who s Who in Electricity Invented battery - Voltaic pile Alessandro Volta

10 Batteries - from Volta to today Anode Cathode

11 Who s Who in Electricity André-Marie Ampère

12 Who s Who in Electricity Georg Ohm

13 Who s Who in Electricity Contributed to: Electric Circuits Spectroscopy Black-body radiation Gustav Kirchhoff

14 Who s Who in Electricity John Ambrose Fleming Vacuum tube diode Russell Ohl Diodes with p-n junctions - Toward modern electronics!

15 Who s Who in Electricity Lee De Forest Triode Transistors (1940s-50s, 50s-60s, and today)

16 Who s Who in Electricity William Shockley Modern transistors - npn and pnp junctions Walter Brattain Integrated circuits - John Bardeen

17 Who s Who in Magnetism William Gilbert Said Earth is magnet with iron core

18 Who s Who in Magnetism Discovered that magnetism can be created by currents Hans Christian Oersted

19 Who s Who in Magnetism Scientist and inventor, AC power, AC motors, wireless transmission Nikola Tesla

20 Who s Who in Magnetism Worked on electricity, optics, relativity Hendrik Lorentz

21 Who s Who in Magnetism Joseph Larmor

22 Who s Who in Magnetism Wilhelm Weber Invented the telegraph (with Gauss) Karl Gauss Numerous contributions to electromagnetic theory

23 Who s Who in Magnetism Discovered effect while graduate student at Johns Hopkins Edwin Hall

24 Who s Who in Magnetism Jean-Baptiste Biot Felix Savart Developed law in 1820

25 Who s Who in Electricity André-Marie Ampère

26 Who s Who in Magnetism Michael Faraday Joseph Henry electromagnets, First Secretary of the Smithsonian

27 Who s Who in Magnetism early studies in bioelectricity, colleague of Volta Luigi Galvani

28 Who s Who in Magnetism Heinrich Lenz

29 Who s Who in Magnetism James Clerk Maxwell one of the greatest physicists of all time, electromagnetism, thermodynamics/ statistical mechanics

30 Who s Who in Optics Heinrich Hertz

31 Who s Who in Optics John Poynting

32 Who s Who in Optics Willebrord Snellius Rene Decartes Thomas Harriot ibn Sahl ~

33 Who s Who in Optics Christiaan Huygens

34 Who s Who in Optics Arthur Compton

35 Who s Who in Optics Lord Rayleigh (John William Strutt)

36 Chapter 21 Electric Announcements Charge and Electric Field PowerPoint Lectures for University Physics, Twelfth Edition Hugh D. Young and Roger A. Freedman Lectures by James Pazun Copyright 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley

37 Forces of Nature All interactions in the entire universe (!) can be described by four forces You ve studied only the gravitational force This semester, we ll do electricity and magnetism Amazingly the two turn out to be part of the same force - the electromagnetic force We ll hint at a third force soon, the last one is covered in Modern Physics class Supermassive black hole at the center of the Milky Way (Sagittarius A)

38 Review of the Gravitational Force Objects have an intrinsic property called mass m An object s mass can be 0 (light - a photon) Two objects with mass attract each other, the force is This works for any two objects: Universal gravitation F is a vector force along line connecting masses (ˆr ) - sign force is attractive (always!) G F = Gm 1m 2 ˆr is a measure of strength of gravitational force ( coupling constant ) G is small Force goes like r 2 Force proportional to mass gravity is very weak 1/r 2 weaker for masses that are further apart more mass means stronger force

39 Electric Charge Objects have another intrinsic property called charge q Greeks learned this by rubbing amber (fossilized tree resin) Greek word for amber = elektron Do Balloons Demo Amber from wikipedia

40 Electric Charge Two kinds of charges Called positive (+) and negative (-) By convention (due to Benjamin Franklin) Objects with charge feel a force Like charges repel, opposites attract This is known from experiment/observation Objects can also be charge neutral Most matter is net charge neutral Neutral matter contains the same amount of positive and negative charges Why is most matter neutral? Benjamin Franklin

41 Matter as Charges Matter is made up of protons, neutrons and electrons The unit of charge is Coulombs: q = e q =0 q = e [q] = Coulombs The charge of a proton is e = (14) C e C Note, Memorize this! m electron m proton m electron m proton

42 Make-up of Atoms m electron m proton Since, they behave very differently! When the charges are free, electrons move much easier than protons They feel the same force (Newton s Third Law pairs), but their acceleration is different! Inside atoms, we think of the lighter electrons orbiting protons like the Earth orbits the Sun This will change when we learn quantum mechanics (Modern Physics) Protons and neutrons reside in the nucleus of the atom F e on p motion F p on e

43 How Do We Know? Electrons discovered in 1897 by Thomson It was thought that the positive charges were distributed evenly throughout the matter (Thomson s plum pudding model) Rutherford experiment 1907 His assistant (Geiger) developed a counter of alpha particles Alpha particles (helium nuclei, discovered in 1895) shot into a foil made of gold, they found more particles bounced backwards than expected Conclusion - Almost all the mass is localized in small regions If an atom was the size of a football stadium, the nucleus would be basketballs at the 50-yard line and the electrons would be in the highest seats Most of what makes up matter (your desk, your fingers,...) is almost entirely empty space!

44 Atoms - Neutrals and Ions Neutral matter is neutral not because it is made up of uncharged particles, but because it is made up of equal numbers of positive and negative charges.

45 The Electric Force How would you determine the electric force between charges? Same way Cavendish did for gravitation in torsional balance! Coulomb measured the electrostatic force (for charges at rest) in Cavendish already did it, but didn t publish! Henry Cavendish Charles-Augustin de Coulomb

46 Coulomb s Law The result (Coulomb s Law) is astounding! F = kq 1q 2 r 2 Looks just like gravitational force! ˆr Finish this Again an inverse square law Mass m => Charge q Gravitational constant G => Coulomb s constant k (electrostatic coupling constant)

47 Chapter 21 Electric Announcements Charge and Electric Field PowerPoint Lectures for University Physics, Twelfth Edition Hugh D. Young and Roger A. Freedman Lectures by James Pazun Copyright 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley

48 Coulomb s Law The result (Coulomb s Law) is astounding! F = kq 1q 2 r 2 Looks just like gravitational force! ˆr Measure with voltmeter Again an inverse and plasma square ball? law Mass m => Charge q Gravitational constant G => Coulomb s constant k (electrostatic coupling constant)

49 Examples of electrical force calculated I A fascinating comparison of gravitational force to electrostatic force is shown in Example 21.1 and Figure Regard Problem-Solving Strategy See also Example 21.2 and Figure

50 Examples of electrical force calculated II Consider Example 21.3 and Figure See also Example 21.4 and Figure

51 Movement of charges charging by conduction Materials that allow easy passage of charge are called conductors. Materials that resist electronic flow are called insulators. The motion of electrons through conducts and about insulators allows us to observe opposite charges attract and like charges repel.

52 Electrons move freely and charges may be induced Take a child s toy, a rubber balloon. If you rub the balloon vigorously on a fuzzy sweater then bring the balloon slowly toward a painted concrete or plaster wall, the balloon will stick to the wall and remain for some time. The electrostatic force between static electrons and the induced positive charge in the wall attract more strongly than the weight of the balloon.

53 Static electricity about an insulator can shift The motion of static charges about a plastic comb and light bits of paper can cause attractive forces strong enough to overcome the weight of the paper.

54 Electric fields may be mapped by force on a test charge If one measured the force on a test charge at all points relative to another charge or charges, an electric field may be mapped. This experiment is often done in one s mind (called a gedanken experiment ).

55 Electric fields I the point charge Fields of force may be sketched for different arrangements of charge. Consider Example 21.6 and Figure

56 Electric fields II charges in motion within a field Consider Example Consider Example 21.8 and Figure

57 Electric fields add as vectors Regard Figure Review Problem-Solving Strategy Follow Example 21.9 and Figure

58 A field around a ring or line of charge Review Example and Figure Review Example and Figure

59 A field around a disk or sheet of charge Review Example and Figure Review Example and Figure

60 Electric field lines map out regions of equivalent force I

61 Electric dipoles and water As mentioned in the introduction, the dipole force of water is vital to chemistry and biology.

62 Consider force and torque on a dipole Regard Figure Follow Example and Figure

63 The electric field of a dipole revisited Consider Example Figure illustrates the example.