About induced current (physics

Be aware that although there is no induced current in the rectangular coil when it is moving at constant speed in the magnetic field, induced emf does exist on the coil.

The basic concept for induced emf to be produced is the "cutting of field lines" by a conductor (it is only that Faraday quantified the "cutting of field lines" into the theory of magnetic flux change in his Law of Electromagentic Induction).

When the rectangular coil is moving inside the magnetic field, its front and back edges, which are two straight conductors, cut through the field lines. You could, using Fleming's Right Hand Rule, determine the "direction" of induced emf at these two conductors. The result is that they (the induced emf) are pointing in the SAME direction, hence cancelling away the effect from each other, and no current would be driven through the coil.

A coil with an acceleration still has induced emf produced at the front and back edges of the coil, beacuse the two edges are continuously cutting field lines. It is only that as the coil picks up velocity, the magnitude of induced emf (both at the two edges) increases correspondingly. A "balanced emf" is thus maintained, and no current would be produced.

It is only under the situation that when one edge of the coil enters into a magneic field of different magnitude (either a stronger or weaker field), the magnitudes of induced emf at the two edges would be different (it is because the cutting of the number of field lines by each edge in a unit time is different). There is then an "unbalanced" emf produced , and a current would then be driven through the coil.

There will be no induced current, assuming that (i) the coil does not change shape, i.e. all points on the coil moves at the same velocity, and (ii) it is not a superconductor. The induced electromotive force is given by

圖片參考：http://imgcld.yimg.com/8/n/HA05726829/o/701104180147513873428480.jpg

Here in the 1st equality, we could pull v x B out of the integral because both v and B are uniform (although v may depend on time). The final loop integral is identically zero because of the fundamental theorem of calculus.

圖片參考：http://imgcld.yimg.com/8/n/HA05726829/o/701104180147513873428491.jpg


Another way to explain this is by saying the magnetic flux through the coil does not change with time regardless whether the coil is accelerating or not. So the induced e.m.f must be zero.

Hope I can help you !


Remember that ,

If there is an induced current , that means an external object affect the

magnetic field with a change of magnetic force .

Also , as an induced current is simply a flow of electric charges , the

magnetic force is relative to the force acting on the moving charge .


What will this present ?

Simply , an accelerative object is moving in the field and the induced current is

also changing .