APPROACHING THE PHAEDRUS

Plato's dialogues are masterpieces of the literary representation of philosophical conversations. Yet the Phaedrus stands out even in Plato's corpus. The dialogue's formal structure makes evident the main topics.1 After the opening scene establishes Ph.'s enthusiasm for Lysias' rhetorical art and S.'s intention to examine it, Ph. reads Lysias' speech on erōs aloud to his companion, whereupon S. delivers extempore two speeches on erōs of his own. Then, just past the halfway point, the dialogue undergoes its most overt change in style and substance as S. shifts from the rhetorical presentations on erōs to a dialectical inquiry into the nature of good discourse. The inquiry is concerned mostly with the art of rhetoric, but concludes with a consideration of written texts and dialectic. Beyond the topics that are given formal prominence – erōs, rhetoric, dialectic, written texts – other important themes that arise in the conversation include philosophy, beauty, play, the soul, the gods, the sophists, and the nature of technē.

Beyond the forms of discourse that structure the dialogue – the rhetorical speeches of the first half, the dialectical inquiry of the second half – S. addresses Ph. in friendly and ironic conversation, in allegories and myths, in didactic argument, in studied artificial language. S. prays; he quotes and invents verse; he mocks sophistic pretenders to rhetorical art.

Like other great works of Greek literature, the Phaedrus comes to us laden with established views and previous interpretations. The dialogue has acquired the additional burden of being considered important, and interpreted accordingly, in accounts of Plato's thought, of the intellectual debates of fourth-century Greece, and of the development of Greek culture and Western metaphysics. There is no better remedy, it seems to me, than an encounter with the dialogue itself. I have attempted to loosen up a bit the constraints of received wisdom and to take a fresh look at what Plato says in this dialogue to his contemporary audience and how he chooses to say it. Furthermore, in the ongoing process of reading and interpreting the Phaedrus, an approach that returns to the dialogue itself would make a timely contribution.

Of the vast secondary literature on the Phaedrus, I cite only those items that seem most useful for understanding whatever point is at issue; this is an economy that should benefit readers of this edition. For questions of syntax, I refer to Guy Cooper's Attic Greek prose syntax (AGPS) because it contains a wealth of informative examples and recognizes significant subtleties that go unremarked in other reference grammars. A new edition of Hermias' commentary on the Phaedrus by C. Lucarini and C. Moreschini (De Gruyter) is still forthcoming as of this writing, and thus could not be used in this edition.

227a1–230e5: PROLOGUE

Two friends, S. and Ph., meet on the street by chance and S. discovers Ph.'s enthusiasm for a speech by Lysias that he has just heard. After S. good-naturedly prods Ph. into admitting that he has a copy of the speech in his possession, they decide to retire to the nearby countryside where they will find relief from the summer heat and Ph. will read the speech to his companion. They converse easily as they walk and when they find a cool pleasant spot underneath a tall plane tree, they assume comfortable positions, the one to read, the other to listen.

The lively and realistic narrative constitutes a prime example of Plato's remarkable literary art. As in the opening of the Republic, the effect is complex: knowing that Plato is in control, the reader is nonetheless lulled into accepting the momentous conversation that follows as arising naturally in consequence of a chance, everyday encounter. All the more remarkable is Plato's ability to convey simultaneously beneath the narrative surface of smooth banter and innocent meandering another quasi-narrative of potentially transformative drama. Taking the measure of Ph.'s character, S. feigns enthusiasm for Lysias' speech in order to entice Ph. into a dialogue on erōs and discourse that will challenge his values and might possibly change his life. Without his being aware of it, Ph. is maneuvered into a position where the attractions of philosophy will make themselves felt.

A professor of mine once opined that the best working experimentalists tended to have a good grasp of basic electronics. Experimental data often come in the form of electronic signals, and one needs to understand how to acquire and manipulate such signals properly. Indeed, in graduate school, everyone had a story about a budding scientist who got very excited about some new result, only to later discover that the result was just an artifact of the electronics they were using (or misusing!). In addition, most research labs these days have at least a few homemade circuits, often because the desired electronic function is either not available commercially or is prohibitively expensive. Other anecdotes could be added, but these suffice to illustrate the utility of understanding basic electronics for the working scientist.

On the other hand, the sheer volume of information on electronics makes learning the subject a daunting task. Electronics is a multi-hundred billion dollar a year industry, and new products of ever-increasing specialization are developed regularly. Some introductory electronics texts are longer than introductory physics texts, and the print catalog for one national electronic parts distributor exceeds two thousand pages (with tiny fonts!).

Finally, the undergraduate curriculum for most science and engineering majors (excepting, of course, electrical engineering) does not have much space for the study of electronics. For many science students, formal study of electronics is limited to the coverage of voltage, current, and passive components (resistors, capacitors, and inductors) in introductory physics.

Introduction

In analog electronics, voltage is a continuous variable. This is useful because most physical quantities we encounter are continuous: sound levels, light intensity, temperature, pressure, etc. Digital electronics, in contrast, is characterized by only two distinguishable voltages. These two states are called by various names: on/off, true/false, high/low, and 1/0. In practice, these two states are defined by the circuit voltage being above or below a certain value. For example, in TTL logic circuits, a high state corresponds to a voltage above 2.0 V, while a low state is defined as a voltage below 0.8 V.

The virtue of this system is illustrated in Fig. 8.1. We plot the voltage level versus time for some electronic signal. If this was part of an analog circuit, we would say that the voltage was averaging about 3 V, but that it had, roughly, a 20% noise level, rather large for most applications and thus unacceptable. For a TTL digital circuit, however, this signal is always above 2.0 V and is thus always in the high state. There is no uncertainty about the digital state of this voltage, so the digital signal has zero noise. This is the primary advantage of digital electronics: it is relatively immune to the noise that is ubiquitous in electronic circuits. Of course, if the fluctuations in Fig. 8.1 became so large that the voltage dipped below 2.0 V, then even a digital circuit would have problems.

Introduction

The silicon controlled rectifier introduced in the last chapter was the first device we have seen that offered some measure of electronic control: the gate current determined the details of the I–V characteristic. This control, however, was fairly limited. In the examples we considered, the gate current determined the time at which the SCR switched to its on-state. Once the SCR was turned on, however, its behavior was no longer related to the magnitude of the gate current, and removing the gate current altogether would not return the SCR to its off-state.

We now turn to a device with a greater measure of electronic control: the transistor. Like the SCR, the transistor allows the user to control a large current through the device with a smaller control signal. But with the transistor, one can have proportional control; that is, the amount of current through the device is proportional to the control signal. This allows one to amplify signals, which is fundamental to all types of electronic communication.

Transistors come in two basic types: bipolar junction transistors (BJTs) and field-effect transistors (FETs). This chapter will cover the fundamentals of BJTs and also introduce some common terminology for transistor amplifiers. FETs are addressed in Chapter 5.

Bipolar transistor fundamentals

A bipolar transistor can be thought of as a sandwich of n-type and p-type semiconductors.

The band theory of solids

Introduction

A fundamental result from basic modern physics is that atoms are characterized by discrete energy levels. Each of these energy levels can accept up to two electrons. When “building” an atom, we start from the lowest level, fill in two electrons, and then move up to the next energy level and fill it with electrons. This continues until we have placed all the atom's electrons in energy levels. We also know that if an atom absorbs energy from the outside (for example, by absorbing a photon), an electron can be promoted to a higher energy level. Conversely, an electron that falls from a higher to a lower energy level emits a photon.

What happens to this energy level model when we assemble many atoms together into a solid? As the atoms get closer together, we must start to talk about the energy levels of the solid as a whole rather than those of the individual atoms. Rather than doing quantum mechanics for an isolated potential (the atom), we do it for a periodic array of atoms that exhibits a periodic potential. The net result of this is that, during the assembly of N atoms, the individual atomic levels split into N levels. This is shown schematically in Fig. 3.1. Thus when the solid is assembled and the atoms are at their final equilibrium spacing, the solid is characterized by a series of energy bands consisting of a large number of closely spaced allowed energy levels.

Chapter 1

1. 1. 1.27 Ω

2. 3a. 100 W

3. 5. I2 = 0.397 A

4. 7. 667 Ω

5. 9. 12.5 Ω

6. 11. I3 = 1.20A

7. 13. Vth = 0.025 V, with positive terminal on the right

8. 15. V2 = 15 V

9. 17. I1 = −1.096 A, I3 = 0.896 A, I5 = 0.086 A

Chapter 2

1. 1. 1.33 μF

2. 3. 8.3 μF

3. 6. magnitude 11.3 kΩ, phase −27.95 degrees

4. 8. 707 rad/s

5. 10. RC = 5.5 × 10−5 s

6. 12. ∣I∣ = 3.36 Arms, phase −9.89 degrees

7. 13. Turns ratio is 1/10, primary current is 0.06 Arms, secondary current is 0.6 Arms

8. 15. Output voltage will be 24 Vrms

9. 16. The output is a 90 Hz sine wave with peak amplitude 0.946V0