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CHAPTER 27. GEOMETRICAL OPTICS
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CHAPTER 28. ELECTROMAGNETIC RADIATION
CHAPTER 29. ÍÏNTEREFERENCE
CHAPTER 30. DIFFRACTION
CHAPTER 31. “HE ORIGIN OF THE REFRACTIVE [NDEX
CHAPTER 32. RADIATION DAMPING. LIGHT SCATTERING
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CHAPTER 33. POLARIZATION
33-5 Optical activity...... . . . Q Q Q Q Q Q k + k> „ «.„ „38-10
CHAPTER 34. RELATIVISTIC EFFECTS IN RADIATION
34-7 The œ,k ÍOUT-VeCEOT........ . Ặ Q23 23+ „+. « 34-16
CHAPTER 3ð. COLOR VISION
CHAPTER 36. MECHANISMS OF SEEING
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CHAPTER 37. (QQUANTUM BEHAVIOR,
CHAPTER 38. “HE RELATION OF WAVE AND PARTICLE VIEWPOINTS
CHAPTER 39. “HE KINETIC 'HEORY OF GASES
CHAPTER 40. “HE PRINCIPLES OF STATISTICAL MECHANICS
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CHAPTER 41. “HE BROWNIAN MOVEMENT
CHAPTER 42. APPLICATIONS OEF KINETIC THEORY
CHAPTER 43. DIFEUSION
CHAPTER 44. “HE LAWS OF THERMODYNAMICS
CHAPTER 45. lLLUSTRATIONS OF THERMODYNAMICS
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CHAPTER 46. RATCHET AND PAWL
CHAPTER 47. SOUND. HE WAVE EQUATION
CHAPTER 48. BEATS
48-1 Adding ÉWO WaVeS...... . Q.33 313333 + + +. 48-1
CHAPTER 49. MODES
CHAPTER 50. HARMONICS
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CHAPTER 5l. WAVES
51-1 PowwWaves........ . HQ Q Q Q Q Q Q22 2212222222222 SIm]
CHAPTER 52. SYMMETRY IN PHYSICAL LAWS
ÏNDEX
NAME ÏNDEX
LIST OF SYMBOLS
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Aforms tra WẪoffOGre
1-1 Introduction
'This two-year course In physics is presented from the point of view that you,
the reader, are going to be a physicist. This is not necessarily the case Of course,
but that is what every professor in every subject assumesl IÝ you are going to be
a physicist, you will have a lot to study: two hundred years of the most rapidly
developing field of knowledge that there is. 5o much knowledge, in fact, that you
might think that you cannot learn all of it in four years, and trulÌy you cannot;
you will have to go to graduate school tool
Surprisingly enouph, ¡in spite of the tremendous amount of work that has been
done for all this time it is possible to condense the enormous mass of results to
a large extent—that is, to fñnd /œws which summarize all our knowledge. Even
so, the laws are so hard to grasp that it is unfair to you to start exploring this
tremendous subject without some kind oŸ map or outline of the relationship of one
part of the subject of science to another. Following these preliminary remarks,
the first three chapters wiïll therefore outline the relation of physics to the rest
of the sciences, the relations of the sciences to each other, and the meaning of
seience, to help us develop a “feel” for the subJect.
You might ask why we cannot teach physics by just giving the basic laws on
page one and then showing how they work in all possible circumstances, as we
do in Euclidean geometry, where we state the axioms and then make all sorts of
deductions. (So, not satisfied to learn physics in Íour years, you want to learn it
in four minutes?) We cannot do it in this way for two reasons. First, we do not
yet knou all the basic laws: there is an expanding frontier of ignorance. Second,
the correct statement of the laws of physics involves some very unfamiliar ideas
which require advanced mathematies for their description. 'Pherefore, one needs a
considerable amount of preparatory training even to learn what the +0ords mean.
No, it is not possible to do it that way. We can only do it piece by piece.
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lach piece, or part, of the whole of nature is always merely an œpprozữmation
to the complete truth, or the complete truth so far as we know it. In fact,
everything we know is only some kind of approximation, because +0e kno+ that
tue do not knou aÌl the laus as yet. Therefore, things must be learned only to be
unlearned again or, more likely, to be corrected.
'The principle of science, the defnition, almost, is the following: The test oƒ
gÌÌ knouledqe is ezperimnent. xperiment 1s the sole 7udge of scientific “truth.”
But what ¡is the source of knowledge? Where do the laws that are to be tested
come from? Experiment, itself, helps to produce these laws, in the sense that it
gives us hints. But also needed is #maginalion to create from these hints the great
generalizations—to guess at the wonderful, simple, but very strange patterns
beneath them all, and then to experiment to check again whether we have made
the right guess. This Imagining process is so dificult that there is a division of
labor in physics: there are #2eoreficœl physicists who imagine, deduece, and guess
at new laws, but do not experiment; and then there are ezperữmnental physicists
who experiment, imagine, deduce, and øuess.
W© said that the laws of nature are approximate: that we fñrst ñnd the “wrong”
ones, and then we ñnd the “right” ones. Now, how can an experiment be “wrong”?
first, in a trivial way: 1ƒ something is wrong with the apparatus that you did
not notice. But these things are easily fxed, and checked back and forth. So
without snatching at such minor things, how can the results oŸ an experiment
be wrong? Only by being inaccurate. For example, the mass oŸ an object never
seems to change: a spinning top has the same weight as a still one. So a “law”
was invented: mass is constant, independent of speed. That “law” is now found
to be incorrect. Mass is found to increase with velocity, but appreciable increases
require velocities near that of light. A frue law is: if an objecb moves with a
speed of less than one hundred miles a second the mass is constant to within one
part in a million. In some such approximate form this is a correct law. So 1n
practice one might think that the new law makes no significant diference. Well,
yes and no. Eor ordinary speeds we can certainly forget it and use the simple
constant-mass law as a good approximation. But for high speeds we are wrong,