PHYS 212 Lecture 7: Current Through a Wire 2/13/17
Document Summary
Charges are separated, so there is a potential energy in a capacitor. Change in potential energy for a charge is: uelec = q v. As capacitor is charged, moves from 0v to vc. Early charges move through smaller potential difference. Finding total energy stored instantaneous charge: q. Dq moves from negative plate to positive plate. Potential energy changes by du = dq * v. Charge a capacitor and remove it from the battery. Electric field points from + to - plate. Place an insulator between the plates insulator becomes polarized (electrons shift slightly) Second e-field in opposite direction, but weaker this makes the internal electric field weaker, but in the same direction. V = e*d inserting an insulator will decrease potential difference, as the electric field is decreased factor of increase is dielectric constant (, kappa) Capacitance increases, because c = q/vc for a vacuum, k = 1, all other insulators, k > 1, air is about 1.
