Ch. 25 Capacitance- 1 farad 1 F = 1 coulomb per volt 1 C/V.- Because we shall consider a number of different geometries, it seems wise to develop a general plan to simplify the work. In brief our plan is as follows: (1) Assume a charge q on the plates; (2) calculate the electric field, E, between the plates in terms of this charge, using Gauss’ law; (3) knowing E, calculate the potential difference V between the plates from Eq. 24-18; (4) calculate Cfrom Eq. 25-1.- Parallel plate capacitor: C increases as area increases and distance between plates decreases.- Capacitors in parallel have the same potential difference (V), which is the same value that their equivalent capacitor has- When a potential difference V is applied across several capacitors connected in parallel, that potential difference V is applied across each capacitor. The total charge q stored on the capacitors is the sum of the charges stored on all the capacitors- Capacitors in series have the same charge (q), which is the same value that their equivalent capacitor has.- When a potential difference V is applied across several capacitors connected in series, the capacitors have identical charge q. The sum of the potential differences across all the capacitors is equal to the applied potential difference V.- The potential energy of a charged capacitor may be viewed as being stored in the electric field between its plates.- In a region completely filled by a dielectric material of dielectric constant k, all electrostatic equations containing the permittivity constant e0 are to be modified by replacing e0 with k´0.Ch. 26 Resistance and Resistivity- 1 ohm 1 = 1 volt per ampere- Ohm’s law is an assertion that the current through a device is always directly proportional to the potential difference applied to the device.- A conducting device obeys Ohm’s law when the resistance of the device is independent of the magnitude and polarity of the applied potential difference.- A conducting material obeys Ohm’s law when the resistivity of the material is independent of themagnitude and direction of the applied electric field.Ch. 27 Circuits- LOOP RULE: The algebraic sum of the changes in potential encountered in a complete traversal of any loop of a circuit must be zero.- RESISTANCE RULE: For a move through a resistance in the direction of the current, the change in potential is -iR; in the opposite direction it is +iR. - EMF RULE: For a move through an ideal emf device in the direction of the emf arrow, the changein potential is +є; in the opposite direction it is -є.- When a potential difference V is applied across resistances connected in series, the resistances have identical currents i. The sum of the potential differences across the resistances is equal to the applied potential difference V- To find the potential between any two points in a circuit, start at one point and traverse the circuit to the other point, following any path, and add algebraically the changes in potential you encounter.- JUNCTION RULE: The sum of the currents entering any junction must be equal to the sum of the currents leaving that junction.- When a potential difference V is applied across resistances connected in parallel, the resistances all have that same potential difference V.- A capacitor that is being charged initially acts like ordinary connecting wire relative to the charging current. A long time later, it acts like a broken