Conceptual Physics Study Notes & Questions: Circuits (Chap. 18)

1. Conceptual Physics Study Notes & Questions: Circuits (Chap. 18) • A closed electric circuit is a continuous line of conductive material through which electric current flows (p374). There must of source of electrical potential difference (voltage)—such as a battery—in order to produce a current flow. Other components in the circuit dissipate this change in potential energy (caused by the battery), by doing work or dissipating the energy in various ways such as light (light bulb) or in the form of heat (electrical resistance). • An open circuit is the same as a closed circuit except that there is a break in the conductive path, breaking off the flow of current. • Measures (p375): • 1 Coulomb, C, is 6.25*1018 electrons. • 1 ampere (I, or amp) is the current flow of 1 Coulomb per second. • 1 volt,V, is a measure of electric potential (i.e. the “pressure” of electrical flow) • Resistance,R, is a measure that reflects the energy dissipation resulting from the flow of electricity through a conductive material. It is measured in ohms. V = IR (Ohm’s Law, p378). • Power, P, is the dissipation of electrical energy per unit time, which is equal to the current flowing through an electric device, times the drop in voltage across its terminals: P = IV (p 379). • The effects of voltage propagate through a conductive medium at nearly the speed of light. But individual electrons move through it very slowly, only a few millimeters per second—this is called the drift velocity. (p375) • Grounding is creating a low resistance path to a commonly shared level of electrical potential—the ground potential. Think of “sea level” and how all water flows down streams and rivers to sea level. In electrical terms, the ground is equivalent to sea level.

2. Its not high voltage that can kill you, its high current. Avoid situations where you can become the low resistance ground path for a high current source (p385). Creating a low resistance ground path is called creating a short circuit (p385). How much current can kill you? • A rectifier, such as a diode, cuts off current flow in one direction. In this way it can convert AC voltage to DC voltage (p386). A transformer converts AC voltage from one level to another (p387). • The most cost effective way to transmit electric power over long distances is by boosting it to a high AC voltage. Why? (p389) • Types of circuits (p391): • Parallel—circuit components are independently attached to a voltage source, that is, all devices have the same voltage across their terminals. Each device has a separate current flowing through it. This is the way electrical power is generally used in your home. • Serial—circuit components are joined along a single conductive line. Each device contributes a voltage drop along the line. The devices all have the same current flowing through them.