Presentation Transcript

1. Electric Fields Review Coulomb’s Law Review Electric Fields Multiple-charge Electric Fields Continuous-charge Electric Fields Parallel Plate Fields Parallel Plate Examples Gauss’s Law
2. Malaysian search Estimate radius from satellite signal strength Heading?? (θ)??? http://m.washingtonpost.com/blogs/worldviews/wp/2014/03/15/possible-paths-for-missing-malaysia-airlines-flight/?tid=HP_more http://www.washingtonpost.com/national/health-science/satellite-locates-malaysian-flight-370-still-flying-seven-hours-after-takeoff/2014/03/15/96627a24-ac86-11e3-a06a-e3230a43d6cb_graphic.html
3. Coulomb’s Law Fundamental property charge Positive and negative charge Units Coulombs (C) Force Law
4. Compare with gravitation Fundamental property mass Positive mass only Units kilograms (kg) Force Law
5. “Field” concept - Gravity Newton’s Universal Law of Gravitation One-step process (tedious) Two-step process (simple)
6. “Field” concept - Electrical Cellphone signal Multiple users sharing same tower. Why calculate each phone separately? 2 step process 1. Calculate common “field”. 2. Calculate each phone’s interaction with that “field”. “Field” equals # of “bars” you have!
7. Electrostatic vs. Gravitational Field In gravitation we calculate Bracket part becomes “g” In electrostatic we calculate Bracket part becomes “E”
8. Electric Field Animation 2-D animation https://ef55311d-a-62cb3a1a-s-sites.googlegroups.com/site/physicsflash/Efield.swf?attachauth=ANoY7crCoduqPW1yrSvMtvv2qNVfA62NqyoNF1X8FY1ldipscty_-KXPmxmMyKYNdrruNd8vROoqOCxqee-i4LdS8Ct27vHfViZ597w8ETuqbnejUPkP7AiKqr4M-S3qn2VLzO2dQNl_KXv-Re0jQ5puGFnzKrPwZvuy0UkMwMU4QhXhJIIX4jWlWsQhQdgzqz-f17N3xQOXvEvfeWC1O-3ObHX89WV72w%3D%3D&attredirects=1
9. Electric Field - Example 16-9 (1) Get magnitudes
10. Electric Field - Example 16-9 (2) XY table
11. Electric Field – Problem 16 Charge square
12. Continuous charge distributions Coulomb’s Law plus a lot of integral calculus! (don’t worry, I’ll just show results) Field of lineof charge Field of ring of charge Field of sheetof charge Field between 2 sheets of charge
13. 1- Field of Line of Charge
14. 2 – Field of Ring of Charge
15. 3 – Field of Sheet of Charge
16. Continuous charge distributions - Summary
17. 4 – Field between 2 Sheetsof Charge In region between parallel plates Note: now the field is constant Coulomb’s Law + Lots of integral calculus = Constant fields (and we just show results)
18. Field between 2 Sheets of Charge In region between parallel plates Note field is constant between plates Uses for parallel plates Capacitors (charge storage) Beam accelerators / deflectors (old TVs, high-energy labs) Semiconductor junctions Photocopy machines
19. Example - Photocopy Field Example 16-6 Electrostatic for twice weight
20. Examples Problem 23 Problem 24
21. Examples Problem 27 Problem 31
22. Field Lines Field lines start at (+) charge, end at (-) charge. Without charge, field lines don’t exist. A (+) test charge moves in the direction of the field lines, a (-) test charge moves opposite the direction of field lines. The cross-sectional density of field lines is proportional to the electric field strength.
23. Gauss’s Law Number of field lines entering or leaving any volume proportional to charge enclosed. Evaluate over entire closed surface Field lines perpendicular to surface Need to know symmetry
24. Gauss’s Law Examples Point charge Line of charge Sheet of charge
25. Gauss’s Law 1 – Point charge Point charge For spherical surface
26. Gauss’s Law 2 – Line charge Line charge For cylindrical surface
27. Gauss’s Law 3 – Sheet charge Sheet charge For pillbox surface