General issues

The primary goals for the 4th edition were

• Correcting errors,
• Making certain difficult sections simpler in units T, Q, E, and C.
• Increasing professors' flexibility by making more chapters optional,
• Adding a graphic classifying each chapter as core, extension, or optional,
• Adjusting chapter lengths to even out the pace (particularly in units T and E),
• Add some new homework problems, and
• Add more end-of-chapter problems to Connect for each unit.

The new graphic appears below each chapter's chapter number in that chapter's opener, and describes how crucial that chapter is for what follows. The main categories are

• Core. These chapters are essential for understanding the unit.
• Extension. These chapters extend the core material in valuable ways, and may be useful for future chapters in the same category, but are not essential and might be dropped.
• Optional. Interesting material not needed for any future chapter.

For the non-core categories, the graphic also supplies information that clarifies the chapter's designation and describes whether and how that chapter depends on others.

UNIT C

This unit has not been changed much for this edition except for chapter C10, which has been refined to make the presentation simpler and clearer. Otherwise, the changes are error fixes and a few new problems.

UNIT N

Unit N has not been changed much in this edition except for error fixes and new problems.

Unit R

Unit R has not been changed much in this edition except for error fixes and new problems.

UNIT E

This the material in this unit has been reorganized to reduce the pace of the more difficult material and give instructors more flexibility in omitting material. Here is a list of important changes:

• Chapter E2 has been shortened and simplified by removing material on how to calculate electric fields using integrals. This material proved difficult and not particularly illuminating for most students. I intend to post on this site a supplement to this chapter containing this material for any professor who feels that teaching these techniques are important.
• The material in chapters E9 and E10 has been reorganized to make chapter E10 optional. Chapter E9 now focuses on the basics of how electrical currents are related to magnetism, and chapter E10 now focuses on applications of these principles in technology. (Chapter E10 is still useful preparation for the spin material in Unit Q.)
• The material in chapter E11 has been simplified to focus less on how one might derive the transformations and more on why these transformations make sense.
• The material in 3rd-edition chapters E12 and E13 has been expanded to three chapters (now E12, E13, and E14) to reduce the pace of this challenging material.
• The 3rd-edition chapter E14 describing the integral forms of Gauss's and Ampere's laws is now chapter E15.
• The material in 3rd-edition chapters E15 and E18 has been expanded to three chapters (now chapters E16, E17, and E18) to reduce the pace of this challenging material.
• The 3rd-edition chapters E16 and E17 now appear as chapters E19 and E20. These were deliberately moved to the end because the old chapter E18 did not depend on this material and tended to get short shrift at the very end of the course. The material in these chapters provides a gentler and (because of the interesting demonstrations that one can do) a more enjoyable end to the course, and the end is also a better place for this optional material.
• The opening sections of chapter E19 have also been simplified to be less mathematical.
• These changes required the creation of many new homework problems, many of which are simpler and/or provide more guidance than the typical problems in the 3rd edition.
• Appendices EA and EB have been removed from the book; they will be posted online for the few people interested in this material. This makes the book less expensive.

UNIT Q

Other than error fixes and a few new problems, the most important changes to unit Q were

• Chapter Q7 no longer provides a mathematical statement of the Time Evolution Rule. This was the most difficult part of an already challenging chapter, and was awkward to state without complex numbers. Chapter Q7 now states the important implications of the rule, pointing the reader to appendix QA (on complex numbers) for a complete statement.
• This deletion required small changes to appendix QA and a number of problems in chapters Q8–Q10 that referred to the Time Evolution Rule. The problems now have a note that they require one to have read appendix QA.
• Appendix QA was also adjusted so that it would fit naturally after chapter Q7 for those courses where the instructor wants to introduce complex numbers.

The current design of the unit also allows an instructor to take a shortcut from chapter Q5 to chapter Q10 for treatment of quantum mechanics that avoids spin (but is necessarily somewhat more superficial). For such a path, the instructor would assign chapters Q9A and Q9B (posted on this site's Resources page) instead of chapters Q6–Q9. This was requested by  several users.

UNIT T

This unit also has been rearranged significantly.

• The end of chapter T4 and the beginning of chapter T5 now include the much simpler material posted earlier on the Resources page of this website (these sections remain posted for users of the 3rd edition).
• The material in the 3rd-edition chapter T6 has been split into chapter T6 (on the Maxwell-Boltzmann distribution) and chapter T7 (on the Planck distribution). The more challenging material in the latter chapter has been made optional.
• Chapter T7–T9 in the 3rd edition are now chapters T8–T10 in the 4th edition.
• The beginning of chapter T9 (3rd edition chapter T8) has been rewritten to make it simpler.
• Chapter T11 on climate change has been thoroughly updated to reflect current events.