Questions and answers with David J. Morin

Since the early 1960s, generations of physics students have been introduced to the concepts of electricity and magnetism (E&M) by physics Nobel laureate Edward Mills Purcell, author of the appropriately titled textbook, Electricity and Magnetism (McGraw Hill, 1963). In 1985 McGraw Hill released a second edition, which became a standard in E&M classes. Then for the next 28 years, the book remained unchanged.

Now, Harvard University physics lecturer David Morin and Cambridge University Press have teamed up on the recently released third edition of the book. Morin is the associate director of undergraduate studies in Harvard’s physics department. He completed his PhD in particle physics at Harvard in 1996, a year before Purcell died. He is also author of the textbook, Introduction to Classical Mechanics: With Problems and Solutions (Cambridge University Press, 2008); his website includes information on his textbooks and links to physics limericks and other physics humor.

Among Morin’s tasks was converting from Gaussian (centimeter-gram-second, CGS) units into SI (meter-kilogram-second, MKS) units—a change that Purcell was initially reluctant to make. Physics Today caught up with Morin to discuss that and other aspects of the new edition.

Morin: I studied from the second edition of Purcell’s book as an undergraduate and I loved it. I was sad to see it fade away over the years due to the fact that very few introductory E&M courses are taught in CGS units nowadays. I had been saying for a long time that someone just needed to change the units to bring the book back into widespread use, and I finally got the push when I found out in the summer of 2010 that I was scheduled to teach our intro E&M course in the upcoming year. To make it easier on my students, I wanted to convert the book, in one way or another, to MKS units for class use. But given that, I figured I might as well add lots of new problems and try to make a new edition. So I contacted Ed Purcell’s sons, Dennis and Frank, and also Cambridge University Press, and everyone was on board. A few days later I learned that plans had changed and I wouldn’t be teaching the E&M course after all, but that short period of scheduling confusion was enough to kick-start the project, so I’m thankful for it!

Morin: Unfortunately, I never got to know Ed Purcell. I wish I had sought him out or bumped into him in the hall at some point during my grad school years. But as the next best thing, I’ve been fortunate to hear many stories about him from Paul Horowitz, coauthor of The Art of Electronics (2nd edition, Cambridge University Press, 1989), who knew him well.

It’s clear from the first two editions of the book that Purcell made great efforts to explain things clearly and completely. So the voice I heard in my head was telling me to explain things in detail and not leave any gaps. I’m sure that some inevitable gaps crept in, but I hope I have lived up to his standards.

Morin: Purcell actually ended up changing his mind about which system of units should be used in the book. In a letter addressed to McGraw Hill and preserved in the Harvard University Archives, dated April 1990, he wrote, “If I do make a third edition it will use only SI units. The intention shocks some of my most respected colleagues, who look on the book as one of the bastions of CGS. But I think a realistic projection calls for that change.”

Independent of one’s views on the different systems of units, the fact is that MKS units have won, at least in introductory courses. So the book could either fade away in CGS units or live on in MKS units. An easy call. But I should note that CGS units still make an appearance in the third edition; I included a number of appendices that discuss the differences between the two systems of units, including 10 pages where every important formula is given in both MKS and CGS units.

Morin: The other main change to the book is the addition of many solved problems. Although reading a book’s text is obviously necessary for getting the basics down, the real understanding comes when a student struggles through solving a problem. I don’t know if the hundreds of new problems will have much of an impact in the classroom; but I do hope that they will have a significant impact on how students learn on their own or in groups outside the classroom, which is after all where most of the learning takes place. Morin: Good question. There are so many factors to consider, I don’t think it’s possible to give a concise answer here—even if I happened to know what the answer was. But personally, after spending such an intense and seemingly endless time polishing up a book for publication, I couldn’t stomach the thought of mixing it all up after only a few years. Ten years seems like a more reasonable time scale, at least for me, given that introductory E&M is an established field. My guess is that a three- or five-year cycle happens mainly with “big production” books, where there is a large team from the publisher working on the book, in addition to the authors. Morin: I have a number of half-finished books sitting on my computer. The next one will be a problem book on freshman mechanics, written for both college and high school students. Then comes a fun little book on probability, and then a textbook on waves. And who knows, maybe a book of physics limericks. Morin: Bill Bryson’s Neither Here Nor There (William Morrow and Co, 1992), for some light reading. It’s been said, quite correctly, that Bryson makes writing look far too easy. I’m also reading Steve Simon’s The Oxford Solid State Basics (Oxford University Press, 2013). I became more interested in the subject after thinking about the real-world applications I added at the end of each chapter of Electricity and Magnetism.