Question: --> how strong is the magnet used in the experiment?
Answer: --> it takes about 4 N to separate it from a thick iron plate.
Answer 2 --> it is not very different from a typical neodymium magnet
that you might have. My guess is that B near the surface
is close to one tesla.
By the way, the magnet is dangerous near a diskette. I carry it in an
iron tube, about 15 cm long. Nothing is attracted to the tube when the
magnet is near its center. I push it in and out with a stick.