(20 1 1? Shaoxing simulation) The picture shows a set of devices designed by Xiao Li to study electromagnets. A magnet is suspended below the spring dynamometer (the lower end of the magnet is the S p

(20 1 1? Shaoxing simulation) The picture shows a set of devices designed by Xiao Li to study electromagnets. A magnet is suspended below the spring dynamometer (the lower end of the magnet is the S pole). (1) According to the current direction in the electromagnet and the winding direction of the coil, it can be determined that the upper end of the electromagnet is the S pole, so it repels the S pole of the magnet under the dynamometer. When the switch is closed, the electromagnets have no magnetism and there is no force between them. After the switch is closed, the electromagnet is magnetic, and the two repel each other, resulting in an upward magnetic force on the magnet, so the indicated value of the dynamometer is reduced.

(2) When the slider P moves to the right, the resistance value of the sliding rheostat connected to the circuit increases, the current in the circuit decreases, the magnetism of the electromagnet weakens, and the repulsive force to the magnet decreases, resulting in an increase in the indicated value of the dynamometer.

(3) According to the requirements of the topic, the force on the slider P can be changed by changing the moving direction of the slider P and making the magnet move in the opposite direction. You can also make the force move in the opposite direction by changing its direction. Because the first method has been ruled out, you can change the direction of the current by changing the positive and negative poles of the power supply, thus changing the direction of the magnetic field of the electromagnets, so that they repel each other and attract each other, causing the magnets to move in opposite directions.

The answer is: (1) smaller; (2) getting bigger; (3) Change the positive and negative poles of the power supply.