PHY 2049 Physics II n n n Coulombs

PHY 2049: Physics II n n n Coulomb’s law, electric field, Gauss’ theorem and electric potential. -W = qΔV Energy conservation applies. F U E V

PHY 2049: Class Quiz If 500 J of work are required to carry a charged particle between two points with a potential difference of 20 V, the magnitude of the charge on the particle is: A. 0. 040 C B. 12. 5 C C. 20 C D. cannot be computed unless the path is given E. none of these

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

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

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

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?

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

n n n 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. k. Qq/a C. k. Qq/a 2 D. 2 k. Qq/a E. 1. 4 k. Qq/a

PHY 2049: Physics II n n n a= 39 cm q 1 = 3. 4 p. C q 2 = 6 p. C E at the center? What is the potential at the center?

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

PHY 2049: Physics II n n 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.

PHY 2049: Physics II

Potential near a sheet charge

PHY 2049: Physics II

HITT n 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 d. 2500 V b. 1600 V c. 2200 V

PHY 2049: Physics II n What is the capacitance of various familiar balls. C = 4πεo. R = 10 -10 R(m) F n n n Basketball-it is an insulator Van de Graff top Earth (radius 6. 4 X 106 m) n CE = 0. 71 m. F

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

PHY 2049: Physics II

PHY 2049: Physics II Ceq = C 1+C 2+C 3

PHY 2049: Physics II

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

PHY 2049: Physics II 25. 20

PHY 2049: Physics II Switch closed on left, capacitor C 1 is being charged We have C 2 = C 3 = 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 C 1 and Ceq = 40. What is the charge on old C 2 and C 3? Is your answer 40 μC? What is your answer if C 2 = 10 μF and C 3 = 30 μF?

PHY 2049: Physics II n n n 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