PHY 2049: Physics II

1. A uniform electric field, with a magnitude of 600 N/C, is directed parallel to the positive x-axis. If the potential at x = 3.0 m is 1 000 V, what is the potential at x = 1.0 m? a. 400 V b. 1 600 V c. 2 200 V d. 2 500 V PHY 2049: Physics II • Coulomb’s law, electric field, Gauss’ theorem and electric potential. • -W = qΔV • Energy conservation applies. U F V E

2. PHY 2049: Class Quiz If 500 J of work are required to carry a charged particle between two points with a potential difference of 20V, the magnitude of the charge on the particle is: A. 0.040C B. 12.5C C. 20C D. cannot be computed unless the path is given E. none of these

3. PHY 2049: Physics II What is the potential at the center point (in units of kq/d) ? a) -7 (b) -5 (c) -7 (d) -7

4. PHY 2049: Physics II Calculate the Electric Field at P Calculate the el. potential at P

5. PHY 2049: Physics II • Point charge • Distribution of charges • Line charge at an edge • Disc on an axis through the center

6. Some old business: What is the electric field of a shell of a uniform spherical charge distribution? What is the potential for each of the above?

7. PHY 2049: Physics II • Some old business The potential of a uniform spherical charge. • Calculate electric field, integrate it to get the potential E r R V V

8. Two particles with charges Q and -Q are fixed at the vertices of an equilateral triangle with sides of length a. The work required to move a particle with charge q from the other vertex to the center of the line joining the fixed particles is: A. 0 B. kQq/a C. kQq/a2 D. 2kQq/a E. 1.4kQq/a

9. PHY 2049: Physics II • a= 39 cm • q1 = 3.4pC • q2 = 6 pC • E at the center? • What is the potential at the center?

10. PHY 2049: Physics II An outline • Capacitors, plate, coaxial, spherical.. • Energy, Dielectric strength, Dielectric constant. • Netweorks: Parallel and Series configuration.

11. PHY 2049: Physics II • Capacitors: A device to hold charge. • It is held by Coulomb force between the charges. +q and –q on two separate places. • V : potential difference: q= CV • C: capacitance units farad.

12. PHY 2049: Physics II

13. PHY 2049: Physics II

14. Potential near a sheet charge

15. Potential near a sheet charge

16. PHY 2049: Physics II

17. PHY 2049: Physics II

18. PHY 2049: Physics II

19. HITT • A uniform electric field, with a magnitude of 600 N/C, is directed parallel to the positive x-axis. If the potential at x = 3.0 m is 1000 V, what is the potential at x = 1.0 m? a. 400 V b. 1600 V c. 2200 V d. 2500 V

20. PHY 2049: Physics II • What is the capacitance of various familiar balls. C = 4πεoR = 10-10 R(m) F • Basketball-it is an insulator • Van de Graff top • Earth (radius 6.4 X 106 m) • CE = 0.71 mF

21. PHY 2049: Physics II • Energy stored in a capacitor U = ½ CV2 = Q2/2C = ½ QV • Dielectric Strength (oops I burned it/broke it) • Capacitor Enhancement by inserting a dielectric: • Replace εo by κεo

22. PHY 2049: Physics II

23. PHY 2049: Physics II Ceq = C1+C2+C3

24. PHY 2049: Physics II

25. PHY 2049: Physics II • Charging and discharging of capacitors. • http://edugen.wiley.com/edugen/instructor/main.uni

26. PHY 2049: Physics II 25.20

27. PHY 2049: Physics II Switch closed on left, capacitor C1 is being charged We have C2 = C3 = 20 μF in parallel. The equivalent capacitor is then Ceq = 40 μF. When the switch is thrown to right, the battery is disconnected, the charge is shared between the capacitors C1 and Ceq = 40. What is the charge on old C2 and C3? Is your answer 40 μC? What is your answer if C2 = 10 μF and C3 = 30 μF?

28. PHY 2049: Physics II • All about capacitors • Capacitance units Farad • C = 4 π κεo R for a sphere of radius R and dielectric constant κ. • Energy stored dielectrics and strength • Parallel and series elements in a network