I have read an article "Remembering Oppenheimer: The Teacher, The Man"  by Edward Gerjuoy, professor of physics emeritus at the University of Pittsburgh. Gerjuoy describes the observation of Oppenheimer he made as a graduate student in the UC-Berkeley physics department from 1938 to 1942. I give here a much-abridged version of Gerjuoy's passages about Oppie's style of teaching (Gerjuoy have called Oppenheimer Oppie since his student days):
Oppie gave no final exams or any other tests. He did not designate a textbook for any of his courses (the hypermodern materials he taught could not be found in any of the then available textbooks). He delivered a class lecture at high speed along with numerous equations written on the board and chain smoking. His relations with his students were surprisingly informal. The seminar was Oppie's domain, his fiefdom. Despite his sometimes overly ferocious questioning, his students respected him and felt indebted to him. ...
The physicist who became Death had a good face as a teacher of physics. Some classmates of mine at a university knew very well about textbooks on physics, and said that one of the best textbooks for electrodynamics was Oppie's. At that time (late 1950s) I sought a Japanese translation of that book at bookstores, but could not find one. I now find an English edition (possibly a revised edition) at Amazon .
By the way, many famous physicists were also a good teacher and ferocious questioner at the seminar. I liked to organize seminars in my work years at an institute and a university, and wanted to be a ferocious questioner, though I may not have been successful in it.
- J. Daintith, et al. ed., Biographical Encyclopedia of Scientists, 2nd edition (Institute of Physics Publishing, Bristol, 1994).
- E. Gerjuoy, APS News, Vol. 13, No. 10, p. 8 (November 2004).
- J. R. Oppenheimer, Lectures on Electrodynamics (Gordon & Breach, 1970) (Out of print--limited availability).