As shown in the figure, there are free moving metal rods PQ and Mn on the two horizontal smooth guide rails. When PQ moves under the action of external force, Mn moves to the right under the action of magnetic force, the movement of PQ may be () A. Uniform acceleration to the right B. uniform acceleration to the left C. uniform deceleration to the right D. uniform deceleration to the left

As shown in the figure, there are free moving metal rods PQ and Mn on the two horizontal smooth guide rails. When PQ moves under the action of external force, Mn moves to the right under the action of magnetic force, the movement of PQ may be () A. Uniform acceleration to the right B. uniform acceleration to the left C. uniform deceleration to the right D. uniform deceleration to the left

Mn moves to the right under the action of magnetic force, which indicates that the magnetic force on Mn moves to the right. According to the left-hand rule, the current points from m to N. according to Lenz's law, the magnetic field producing induced current in the coil should decrease upward or increase downward. According to the right-hand rule, PQ may accelerate to the left or decelerate to the right

As shown in the figure, there are free moving metal rods PQ and Mn on the two horizontal smooth guide rails. When PQ moves under the action of external force, Mn moves to the right under the action of magnetic force, the movement of PQ may be ()
A. Uniform acceleration to the right B. uniform acceleration to the left C. uniform deceleration to the right D. uniform deceleration to the left

Mn moves to the right under the action of magnetic force, which indicates that the magnetic force on Mn moves to the right. According to the left-hand rule, the current points from m to N. according to Lenz's law, the magnetic field producing induced current in the coil should decrease upward or increase downward. According to the right-hand rule, PQ may accelerate to the left or decelerate to the right

As shown in the figure, the solenoid with constant current is placed between the smooth parallel metal guide rails of Mn and PQ, and the two metal rods AB and CD are placed on the guide rails respectively. When the current through the solenoid changes, the movement of the rods AB and CD is as follows: ()
A. When the current increases, AB and CD are close to each other. B. when the current increases, AB and CD must be separated. C. when the current decreases, AB and CD must be separated. D. when the current decreases, AB and CD are close to each other

When the current of the circuit increases, the magnetic field of the coil increases. According to the ampere rule, the magnetic field direction of the coil can be determined by the current direction, which is perpendicular to the rail upward. Because the coil is in the middle of the two rods, the magnetic flux passing through the two rods becomes larger. According to Lenz's Law: increase, reverse and decrease, the wire frame abdc can be obtained Finally, according to the left-hand rule, the direction of Ampere force can be determined: ab rod is in the vertical downward magnetic field, and the current direction Ba, then the direction of Ampere force is to the left. CD rod is in the vertical downward magnetic field, and the current direction DC, then the direction of ampere force is to the right. Therefore, the two are separated; therefore, a is wrong, B is correct; when the current of the circuit becomes smaller, the coil is closed According to the ampere rule, the magnetic field direction of the coil can be determined by the current direction, which is perpendicular to the rail upward. Because the coil is in the middle of the two rods, the magnetic flux passing through the two rods becomes smaller. According to Lenz's Law: increasing reverse decreasing the same, we can get the wire frame abdc Finally, according to the left-hand rule, the direction of Ampere force can be determined: ab rod is in the vertical downward magnetic field, and the current direction AB, then the direction of Ampere force is right. CD rod is in the vertical downward magnetic field, and the current direction CD, then the direction of Ampere force is left. Therefore, the two are close to each other; therefore, C is wrong, D is correct; therefore, BD is selected

As shown in figure (a), the smooth and long enough parallel metal guide rails Mn and PQ are fixed on the same horizontal plane, the distance between the two guide rails L = 0.2m, the resistance R = 0.4 Ω, a metal rod with mass m = 0.1kg and resistance R = 0.1 Ω is placed on the guide rail, the resistance of the guide rail can be ignored, the whole device is in the uniform magnetic field with magnetic induction intensity B = 0.5T, and the magnetic field direction is vertical and downward If the indication U of the ideal voltmeter changes with time t, the relationship is shown in figure (b)
(1) Try to analyze and explain the movement of the metal rod; (2) calculate the instantaneous power of the external force F at the end of the second second second

(1) The voltage expression number is u = IR = blrr + RV & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp