As shown in the figure, the smooth U-shaped metal frame is still on a horizontal plane in a vertical downward uniform magnetic field. Now the AB rod suddenly obtains an initial velocity V and moves to the right A. B. the current in the circuit decreases uniformly. C. the potential of point a is lower than that of point B. D. the U-shaped frame moves to the right

As shown in the figure, the smooth U-shaped metal frame is still on a horizontal plane in a vertical downward uniform magnetic field. Now the AB rod suddenly obtains an initial velocity V and moves to the right A. B. the current in the circuit decreases uniformly. C. the potential of point a is lower than that of point B. D. the U-shaped frame moves to the right

ABC and bar have initial velocity to the right. According to the right-hand rule, the current from B to a is generated, and the potential of point a is higher than that of point B. according to the left-hand rule, the ampere force moves to the left, and the bar AB decelerates. Because the electromotive force decreases and the current decreases, the ampere force decreases. According to Newton's second law, the acceleration decreases, and the acceleration decreases Therefore, a, B and C are wrong. When D and ab rods move to the right, the magnetic flux of the circuit increases. According to Lenz's law, it can be judged that the smooth U-shaped metal frame also moves to the right, which can prevent the magnetic flux of the circuit from increasing