1. PHY 2049: Physics II Tutoring Center is open in room NPB 1100, M-F 10:00AM -3:00PM. It is free. Hopefully all webassign problems have been solved. Please see me immediately after the class if there is still an issue.

2. PHY 2049: Physics II About bicycle riding: If some one shows you a trick, it means that, It is possible to do that trick The person who showed you, can do the trick. It does not mean that you can do the trick. Try it a lot of times and you can too.

3. Electric fields from different geometrical objects. wires Rings and disks Planes Another algorithm Al-Khwarizmi the Persian astronomer and mathematician, wrote a treatise in Arabic in 825 AD, On Calculation with Hindu Numerals, which was translated into Latin in the 12th century as Algoritmi de numero Indorum[1], which title was likely intended to mean "Algoritmi on the numbers of the Indians", where "Algoritmi" was the translator's rendition of the author's name; but people misunderstanding the title treated Algoritmi as a Latin plural and this led to the word "algorithm" (Latin algorithmus) coming to mean "calculation method". The intrusive "h" is most likely due to a false cognate with Greek αριθμος arithmos = "number". mathematicianArabic[1]Greek (wikipedia: http://en.wikipedia.org/wiki/Algorithm#Etymology

4. PHY 2049: Physics II Flux and Gauss’ theorem

5. PHY 2049: Physics II Gaussian (imaginary) surfaces Flux = Φ = ∑ E.dA E.dA for a cube is easy to visualize. Let calculus do it for a sphere or any other shape. Φ c = q total /ε o

6. S 1 : Φ c = q/ ε o S 2 : Φ c = -q/ ε o S 3 : Φ c = 0 S 4 : Φ c = 0

7. For a cylinder with axial field, no contribution to flux from the side walls. From the far top, >0 Near (bottom), <0

8. PHY 2049: Physics II No force/field from the charge outside On inside circle E.4πr 2 =q/ε o Coulomb’s law Very outside, E = k 5q/r 2 P + + + + + +

9. PHY 2049: Physics II The electric field in a metal is zero Charge +q on inside surface. Because it is neutral, outside surface must be -q.

10. PHY 2049: Physics II Electric field is radial. E.A = 0 for the top and bottom surfaces. Sideways: E 2πrh = λh/ε 0 E = λ/ 2πrε 0

11. PHY 2049: Physics II Plane 2EA = σA/ε o E = σ/2ε o

12. PHY 2049: Physics II E = σ/ε o inside

14. PHY 2049: Physics II Gauss’ theorem Electric fields due to a point charge (Coulomb’s), a wire and a plane. Charge shells don’t act inside. In an insulator with uniformly distributed charge, only charge enclosed contributes to the field.