As of now, one of the Physics 8B lectures is full, but the other has 12 spaces open (though 11 of the open lab spaces are in W 4-6pm).
There are three Physics 7B lectures. One is full, one at (TuTh 8-9:30am) has 46 spaces open, and one has 9 spaces open (with most of the open lab spaces at Tu 8-10am or Th 8-10am). There is also a Physics H7B (honors course) with 21 open spaces (out of 25 total).
Physics 7B can substitute for Physics 8B, according to the
MCB handbook. However, this is generally considered to be the "harder" physics course for physics and engineering majors, and requires Math 53 (multivariable calculus) as at least a co-requisite.