(1) As can be seen from the figure, the current direction in the electromagnet is to the right. According to Ampere's law, terminal A is the N pole and terminal B is the S pole.

(2) When the slider of the sliding rheostat moves to the left, the resistance of the sliding rheostat decreases, the current in the circuit increases, and the number of needles at the lower end of the electromagnet increases, indicating that the magnetic induction intensity of the electromagnet is related to the current when the number of coil turns is constant;

(3) In Figure B, two electromagnets are connected in series with the same current. The two big nails are the same, and the iron core of the electromagnet is the same, but the number of turns of the coil is different. The more turns, the more nails are attracted, which means the stronger the magnetism. However, when the current is constant, the magnetic field strength of the electromagnet is also related to the number of turns of the coil.

So the answer is: (1) north (or n); (2) Current scale; (3) The number of turns of the coil.