About shaking a coil between the magnets

Mon, Sept 24, 2007 at 7:26 PM

This is what I got after a long, hard investigation on the common phenomena.
What we usually ignore is the variation of effort of our hand in shaking the EM-coil, the difference between the difference in each shake wouldn’t be great unless the coil is winded 2000 times. i.e. We use a Force F to shake the EM coil, but at one shake we used F+s1; while at another shake we may use F+s2. Can we tell the difference between s1 and s2? We need equipment with sensitivity related to the parameters of the EM coil(inductance, mass of coil, resistance, strength of magnetic field of the magnet……)
The following is a simplified discussion with EM-coil within 2 magnets.
When we push a EM-coil toward the magnet, a motion EMF would be generated at the coil. And this motion EMF would produce a EMF in the opposite direction of where we push the magnet. Since originally there are no electrical current flowing in any direction in the EM coil, thus electrical current is flowing in the same direction of motion EMF(The only EMF exist in this EM-coil.) Thereby magnetic poles will be formed at 2 ends of the EM-coil which oppose the motion of the EM-coil( i.e. Approaching side: same as the magnet pole face it, Departing side: opposite of the magnet pole face it) However, as the electrical current begin to flow, self-inductance modify the build up of magnetic poles in the EM coil to be ‘gradual’. As soon as magnetic pole is formed in EM coil, the resistance of the EM coil could be felt.
Now it depend on how does our nervous system reacting to that. Supposedly, we could adjust the power of our hand so the net force acting on the EM-coil will remain the same(Unlimited Power Supply), or we supplied the same force despite the resistance(Fixed but limited Power supply). Our hand is an sensitivity equipment to the subtle/rapid variation of the resisting force. And how we react to it lies outside the scope of discussion here.
In either case, there are now 3 factors acting on the EM-coil: the strength of magnetic poles formed in the EM-coil(directly relate to the acceleration of the EM-coil, varied with square of distance), the effect of changing amount of electrical current flowing in the EM coil(self-inductance), and the Force supplied by our hand. The first one would always act in the opposite direction of the last item, an indirectly related the last item. And the second item is always the opposite of the change of the first item. The net result of 1 iteration would resulted as the appropriate amount of electrical current flow in the EM-coil, then the same cycle repeat itself throughout the process. (The number of the cycle depend on the minimum time taken for each process to react.) Notice that the first item is directly proportional to the velocity of the EM coil, and velocity is the accumulation of many acceleration caused by 1 and 3 item.
Suppose we talk about the former case, as we move then electrical current begin to flow, magnetic poles begin to build up in the EM coil, magnetic poles will appears in the ends of EM coil whatever how small is the electrical current. Self inductance kicks in and slow down the forming of magnetic poles. ( i.e. the expected strength of magnetic poles in EM coil would be greater than the actual EM coil.) Then this relatively weak magnetic pole begin to interact with the magnet and caused a resistance force. This case here assume all resistive force is cancelled by hand.( i.e. the hand has to shake the EM coil harder.) Taken into consideration of the above iteration, the consequence is the resistive force is getting stronger as the EM-coil approach the magnet. (This scenario is similar to how traditional generator produce electrical current. Notice that we force the cancellation of 1 and 3 item, some intricacy of this phenomena is thus lose. It sort of become a ‘damped oscillation’ in SHM)
Now we are talking about the later scenario which the force supplied is limited, i.e. the net force acting on the EM-coil is varied in according to the distance from the magnet.(The closer is the distance, the stronger is the reaction.) As we move then electrical current begin to flow, magnetic poles begin to build up in the EM coil, magnetic poles will appears in the ends of EM coil opposing the movement. Self-inductance takes a greater role in the process, and has stronger effect on modifying factor 1 and 3. The resistive force has the effect of weaken itself through the iteration, less resistive force is experience. The intricacy/complexity of the process is thus preserved. And the process iterate through interaction of factor 1,2 and 3; producing variation of voltage and resistive force.(Note each iteration is NOT independent of each other. Steady state may not exist at all.)

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