Presentation on theme: "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."— Presentation transcript:
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.
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.
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, 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". mathematicianArabicGreek (wikipedia:
PHY 2049: Physics II Flux and Gauss’ theorem
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
S 1 : Φ c = q/ ε o S 2 : Φ c = -q/ ε o S 3 : Φ c = 0 S 4 : Φ c = 0
For a cylinder with axial field, no contribution to flux from the side walls. From the far top, >0 Near (bottom), <0
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
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.
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
PHY 2049: Physics II Plane 2EA = σA/ε o E = σ/2ε o
PHY 2049: Physics II E = σ/ε o inside
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.