The Washington Post published a ranking of college majors by the number of number of hours students study outside of class, and physics ranked third out of the 29 majors listed (the data were taken from the National Survey of Student Engagement). At 19.7 hours per week, physics ranked behind architecture (23.7 hours) and chemical engineering (21.6 hours). Chemistry was fourth at 18.4 hours. Near the bottom of the ranking are communications (12.5 hours) and marketing (12.1 hours).
These results would not come as any surprise to physics professors, who already recognize that the miasma of undergraduate mediocrity that infects many universities is a serious obstacle to excellence in physics learning. In fact, the colleague who shared the Post article with me complained that one of the reasons for the high attrition rate among physics majors is that some students who have the ability to succeed refuse to work hard enough to do so.