✔ 最佳答案
Assume, in a simple example, that a metallic straight rod is moving horizontally across a magnetic field with field lines vertically downward, such that the velocity of the rod is both normal to the longitudinal axis of the rod and the field line direction. In other words, the length of the rod, field lines and velocity vector are mutually perpendicular.
The rod is connected to an external circuit so that current could flow if there exist and induced emf.
1. This happens when the rod is moving at a constant speed across a constant (in time) and uniform (in space) magnetic field. The induced emf is constant and hence the induced current is also constant independent of time.
2. This happens when the rod is under a constant acceleration, such that its speed increases linearly with time. Since induced emf is proportional to the speed of the rod, hence the induced emf increases linearly with time.
Another scenario is that the rod is moving at constant speed, but at a field with strength that increases (or decreases) uniformly in space. The induced emf and induced current thus increases uniformly with time.
3. Either the rod is moving with a non-uniform acceleration in a uniform field or the field strength increases (or decreases) in a non-uniform rate in space. Under such situation, the induced emf and current increases in a non-uniform rate.
