As shown in the figure, a parallel metal guide rail with no resistance is placed in the uniform magnetic field. The guide rail is connected with the large coil m, and a wire AB is placed on the guide rail. The magnetic induction line is perpendicular to the plane of the guide rail. In order to make the small closed coil n surrounded by M produce clockwise induced current, the motion of the wire may be () A. Moving to the right at a constant speed B. accelerating to the right C. decelerating to the right D. accelerating to the left

As shown in the figure, a parallel metal guide rail with no resistance is placed in the uniform magnetic field. The guide rail is connected with the large coil m, and a wire AB is placed on the guide rail. The magnetic induction line is perpendicular to the plane of the guide rail. In order to make the small closed coil n surrounded by M produce clockwise induced current, the motion of the wire may be () A. Moving to the right at a constant speed B. accelerating to the right C. decelerating to the right D. accelerating to the left

A. When the wire AB moves to the right at a constant speed, the induced electromotive force and induced current generated by the wire AB remain constant, the magnetic field generated by the large coil m remains constant, and the magnetic flux passing through the small coil n remains constant, so there is no induced current generated; B. When the wire AB accelerates to the right, the induced electromotive force and induced current generated in the wire AB increase. According to the right-hand rule, the direction of AB current is from a to B. according to the ampere rule, the direction of magnetic field generated by M is perpendicular to the paper surface, and the magnetic flux passing through n increases. According to Lenz's law, the induced current generated by coil n is counterclockwise, which is not in line with the meaning of the problem So B is wrong; C. When the wire AB decelerates and moves to the right, the induced electromotive force and induced current generated in the wire AB decrease. According to the right-hand rule, the direction of AB current is from a to B. according to the ampere rule, the direction of magnetic field generated by M is perpendicular to the paper surface and inward, and the magnetic flux passing through n decreases. According to Lenz's law, the induced current in the clockwise direction generated by coil n is consistent with the meaning Correct. & nbsp; & nbsp; & nbsp; & nbsp; D. When the wire AB accelerates to the left, the induced electromotive force and induced current generated in the wire AB increase. According to the right-hand rule, the direction of AB current is from B to A. according to the ampere rule, the direction of magnetic field generated by M is perpendicular to the paper surface and outward, and the magnetic flux passing through n increases. According to Lenz's law, the induced current in the clockwise direction generated by coil n is consistent with the meaning of the problem Correct. So select CD

Which resistance is greater, copper or iron?

Ask questions with conditions
Should ask: copper and iron in the same size, the same environment, which resistance?
A more accurate question should be: copper and iron, which one has high resistivity?
The answer is: iron
For example, the resistance of very thick iron wire is smaller than that of very thin copper wire. For another example, the resistance of iron at high temperature is smaller than that of copper at low temperature