Hefei Spring Consulting Recruitment Information

According to Ampere's rule, the bending of the four fingers of the right hand points to the current direction, and the direction pointed by the thumb-the upper end of the energized solenoid is N pole. According to the interaction between magnetic poles, the energized solenoid and bar magnet show attractive force, and the spring is elongated.

When the switch S is closed, the current only passes through the lower resistance. When the switch S 1 is closed again, the total resistance of the parallel circuit is smaller than any other resistance, so the resistance in the connected circuit becomes smaller, the current becomes larger, the magnetism of the energized solenoid becomes larger, the attraction between the solenoid and the bar magnet becomes larger, and the spring becomes longer, so the spring becomes longer.

So the answer is: n; Get longer.