The Directions Of Currents we drew the current arrows in the direction in which positively charged particles would be forced to move through the loop by the electric field. Such positive charge carriers, as they are often called, would move av.cy from the positive battery terminal and toward the negative terminal. Actually, the charge carriers in […]
Electric Current Ia reminds us, an isolated conducting loop-regardless of whether it has an excess charge-is all at the same potential. No electric field can exist within. it or along its surface. Although conduction electrons are available, no net electric force acts on them and thus th re is no current. If, as in , we insert […]
Moving Charges and Electric Currents Chapters 22 through 26 deal largely with- electrostatics-that is, with charges at rest. With this chapter we begin to focus on electric currents-that is, charges in motion. examples of electric currents abound, ranging from the large currents that constitute lightning strokes to the tiny nerve currents that regulate’nor muscular activity. […]
Dielectrics and Gauss’ Law In our discussion of Gauss’ law in Chapter 24, we assumed that the charges existed in a vacuum. Here we shall see how to modify and generalize that law if dielectric materials, such as those listed in Table 26-1, are present. shows a parallel-plate capacitor of plate area A, both with and without a […]
Dielectrics An Atomic View What happens, in atomic and molecular terms, when we put a dielectric in an electric field? There are two possibilities. depending on the nature of the molecules: 1. Polar dielectrics. The molecules of some dielectrics, like water, have permanent electric dipole moments. In such materials (called polar dielectrics), the electric dipoles tend […]
Energy Stored in an Electric Field Work must be done by an external agent to charge a capacitor. Starting with an uncharged capacitor, for example, imagine that-using “magic tweezers”-you remove electrons from one plate and transfer them one at a time to the other plate. The electric field that builds up in the space between the plates has […]
A Cylindrical Capacitor in cross section, a cylindrical capacitor of length L formed by two coaxial cylinders of radii a and b. We ‘assume that L ~ b so that we can neglect the fringing of the electric field that occurs at the ends of the cylinders. each plate contains a charge of magnitude q. As a Gaussian […]
Calculating the Capacitance Our task here is to calculate the capacitance of a capacitor once we know its ometry. Because we will 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: (I) Assume a charge q on the plates; (2) calculate […]
The Uses of Capacitors You can store energy as potential energy by pulling a bowstring, stretching a spring, compressing a gas, or lifting a book. You can also store energy as potential energy in an electric field, and a capacitor is a device you can use to do exactly that. There is a capacitor in a […]
Capacitance During ventricular fibrillation, a common type of heart attack, the chambers of the heart fail to pump blood because their muscle fibers randomly contract and relax. To save a victim of ventricular fibrillation, the heart muscle must be shocked to reestablish its normal rhythm. For that, 20 A of current must be sent through […]