Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] Introductory Circuit Analysis, 12/e Boylestad Chapter 4 Ohm’s Law, Power, and Energy

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OBJECTIVES Understand the importance of Ohm’s law and how to apply it to a variety of situations. Be able to plot Ohm’s law and understand how to “read” a graphical plot of voltage versus current. Become aware of the differences between power and energy levels and how to solve for each. Understand the power and energy flow of a system, including how the flow affects the efficiency of operation. Become aware of the operation of a variety of fuses and circuit breakers and where each is employed.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OHM’S LAW The first equation to be described is without question one of the most important to be learned in this field. It is applicable to dc circuits, ac circuits, digital and microwave circuits, and, in fact, any type of applied signal. In addition, it can be applied over a period of time or for instantaneous responses. The equation can be derived directly from the following basic equation for all physical systems:

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OHM’S LAW Every conversion of energy from one form to another can be related to this equation. In electric circuits, the effect we are trying to establish is the flow of charge, or current. The potential difference, or voltage, between two points is the cause (“pressure”), and the opposition is the resistance encountered.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OHM’S LAW In summary, therefore, the absence of an applied “pressure” such as voltage in an electric circuit will result in no reaction in the system and no current in the electric circuit. Current is a reaction to the applied voltage and not the factor that gets the system in motion. To continue with the analogy, the greater the pressure at the spigot, the greater is the rate of water flow through the hose, just as applying a higher voltage to the same circuit results in a higher current.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OHM’S LAW

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OHM’S LAW FIG. 4.2 Basic circuit.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OHM’S LAW FIG. 4.3 Defining polarities.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] OHM’S LAW FIG. 4.4 Example 4.3. FIG. 4.5 Example 4.4.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] PLOTTING OHM’S LAW Graphs, characteristics, plots, and the like play an important role in every technical field as modes through which the broad picture of the behavior or response of a system can be conveniently displayed. It is therefore critical to develop the skills necessary both to read data and to plot them in such a manner that they can be interpreted easily.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] PLOTTING OHM’S LAW FIG. 4.6 Plotting Ohm’s law.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] PLOTTING OHM’S LAW FIG. 4.7 Demonstrating on an I-V plot that the lower the resistance, the steeper is the slope.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] PLOTTING OHM’S LAW FIG. 4.8 Applying Eq. (4.7).

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] PLOTTING OHM’S LAW FIG. 4.9 Example 4.5.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] PLOTTING OHM’S LAW This diode ideally acts as a low- resistance path to current in one direction and a high-resistance path to current in the reverse direction, much like a switch that passes current in only one direction.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] PLOTTING OHM’S LAW FIG Semiconductor diode characteristics.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] POWER In general, the term power is applied to provide an indication of how much work (energy conversion) can be accomplished in a specified amount of time; that is, power is a rate of doing work.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] POWER Since energy is measured in joules (J) and time in seconds (s), power is measured in joules/second (J/s). The electrical unit of measurement for power is the watt (W), defined by:

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] POWER In equation form, power is determined by:

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] POWER FIG Defining the power to a resistive element. FIG Example 4.6.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] POWER The power associated with any supply is not simply a function of the supply voltage. It is determined by the product of the supply voltage and its maximum current rating.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] POWER FIG The nonlinear I-V characteristics of a 75 W light bulb (Example 4.8).

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] ENERGY For power, which is the rate of doing work, to produce an energy conversion of any form, it must be used over a period of time. The energy (W) lost or gained by any system is therefore determined by:

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] ENERGY

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] ENERGY Note that the energy in kilowatthours is simply the energy in watthours divided by To develop some sense for the kilowatthour energy level, consider that 1 kWh is the energy dissipated by a 100 W bulb in 10 h. The kilowatthour meter is an instrument for measuring the energy supplied to the residential or commercial user of electricity.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] ENERGY FIG Kilowatthour meters: (a) analog; (b) digital. (Courtesy of ABB Electric Metering Systems.)

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] ENERGY FIG Cost per kWh and average kWh per customer versus time. (Based on data from Edison Electric Institute.)

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] ENERGY TABLE 4.1 Typical wattage ratings of some common household items.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] EFFICIENCY A flowchart for the energy levels associated with any system that converts energy from one form to another is provided in Fig Note that the output energy level must always be less than the applied energy due to losses and storage within the system. The best one can hope for is that W out and W in are relatively close in magnitude.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] EFFICIENCY Conservation of energy requires that –Energy input = energy output + energy lost or stored by the system FIG Energy flow through a system.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] EFFICIENCY FIG Basic components of a generating system.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] EFFICIENCY FIG Cascaded system.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] CIRCUIT BREAKERS, GFCIs, AND FUSES The incoming power to any large industrial plant, heavy equipment, simple circuit in the home, or meters used in the laboratory must be limited to ensure that the current through the lines is not above the rated value. To limit the current level, fuses or circuit breakers are installed where the power enters the installation, such as in the panel in the basement of most homes at the point where the outside feeder lines enter the dwelling.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] CIRCUIT BREAKERS, GFCIs, AND FUSES FIG Fuses: (a) CC-TRON® (0–10 A); (b) Semitron (0–600 A); (c) subminiature surface-mount chip fuses.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] CIRCUIT BREAKERS, GFCIs, AND FUSES In homes built in recent years, fuses have been replaced by circuit breakers. When the current exceeds rated conditions, an electromagnet in the device will have sufficient strength to draw the connecting metallic link in the breaker out of the circuit and open the current path.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] CIRCUIT BREAKERS, GFCIs, AND FUSES FIG Circuit breakers.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] CIRCUIT BREAKERS, GFCIs, AND FUSES The most recent National Electrical Code requires that outlets in the bathroom and other sensitive areas be of the ground fault circuit interrupt (GFCI) variety; GFCIs are designed to trip more quickly than the standard circuit breaker. FIG Ground fault circuit interrupter (GFCI): 125 V ac, 60 Hz, 15 A outlet.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] APPLICATIONS Fluorescent versus Incandescent FIG A 23 W, 380 mA compact fluorescent lamp (CFL).

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] APPLICATIONS Fluorescent versus Incandescent TABLE 4.2 Comparison of the lumens generated by incandescent and fluorescent bulbs.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] APPLICATIONS Fluorescent versus Incandescent FIGURE 4.25 Internal construction of the CFL of Fig

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] APPLICATIONS Microwave Oven FIG Microwave oven.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] APPLICATIONS Household Wiring The one specification that defines the overall system is the maximum current that can be drawn from the power lines since the voltage is fixed at 120 V or 240 V (sometimes 208 V). For most older homes with a heating system other than electric, a 100 A service is the norm. Today, with all the electronic systems becoming commonplace in the home, many people are opting for the 200 A service even if they do not have electric heat.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] APPLICATIONS Household Wiring FIG A service conductors: (a) 4/0 aluminum and 2/0 copper; (b) three-wire 4/0 aluminum service.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] COMPUTER ANALYSIS FIG Circuit to be analyzed using PSpice and Multisim.

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] COMPUTER ANALYSIS PSpice FIG Using PSpice to determine the voltage, current, and power levels for the circuit in Fig

Introductory Circuit Analysis, 12/e Boylestad Copyright ©2011 by Pearson Education, Inc. publishing as Pearson [imprint] COMPUTER ANALYSIS Multisim FIG Using Multisim to determine the voltage and current levels for the circuit of Fig