## OneOwOne 2 years ago Len'z law when a magnet passes through a coil it would induce current that will create a magnet field that is opposite of the magnet's pole. Will the magnetic field created by the coil be strong enough to cancel out the motion of the magnet? Or even stop it while the magnet is coming closer and closer? In other words, will the input Kinetic energy of the magnet be converted to electrical energy and cancel out the magnet's motion? Or weaken it? @radar @Mashy

1. OneOwOne

@Vincent-Lyon.Fr

2. Visionary01

Hard to imagine what will happen. But good luck!

3. Visionary01

I myself I'M LOST in the world of electromagnetism. But you mentioned good people to help out!

4. Vincent-Lyon.Fr

What do you mean by : "when a magnet passes through a coil it would induce current that will create a magnet field that is opposite of the magnet's pole." In my view this is not true. When the magnet approaches the coil, the current in the coil creates an induced B-field that will repel the magnet (fields in opposite directions), BUT when the magnet has crossed the coil and when it is getting away from it, then the current in the coil induces a field that is attracting the magnet (fields in same direction). In both cases, the force acting on the magnet will slow it down. If it comes to halt or not, will depend on the initial velocity of the magnet, provided no other forces are acting on it.

5. OneOwOne

@Vincent-Lyon.Fr Yes but in this case, the coil will turn to an electromagnet...The force of the B field generated by the coil will be = or less by a little to the force applied by the manget. Thus will cause it to slow or even stop. If no force is being applied to it.

6. OneOwOne

What if the magnet had a weaker force applied to it OTHER than the coil, will the magnet be able to "break free"? And do that quickly? Like dropping a magnet down a tube copper wire, due to gravity it moves down. But... gravities force is strong enough to make the magnet move. All in all imagine a magnet coming closer to the coil at a speed 100 M/S and due to that coil the magnet will significantly lose that speed, because of the powerful force resisting the magnets motion...

7. Vincent-Lyon.Fr

"Yes but in this case, the coil will turn to an electromagnet...The force of the B field generated by the coil will be = or less by a little to the force applied by the manget. Thus will cause it to slow or even stop. If no force is being applied to it." This is nonsensical ;-) 1. Forces that apply to DIFFERENT systems do NOT add up 2. A system is not subject to its own field

8. OneOwOne

Um @Vincent-Lyon.Fr What will happen in this situation? A magnet at high speeds approaching and could pass through a coil?

9. Vincent-Lyon.Fr

Definitely.

10. Mashy

it could definitely pass through a coil.. but its k.E. would decrease.. where did the energy go?.. energy got converted into electrical energy

11. OneOwOne

Makes sense. Thanks all!

12. OneOwOne

@Vincent-Lyon.Fr Since the coil will apply an opposite force to he magnet, and the magnet had another force aslo applied to it, and that force is the initial one that caused the magnet to pass through the coil at the beginning, what do you think can happen? @Mashy

13. Mashy

what you mean HAD a force... we don't worry about HAD a force.. cause once force is gone.. its effect is gone.. !! anyways.. as i mentioned earlier.. it would just decelerate .. thats all :-/

14. OneOwOne

@Mashy Let say you pushed the magnet in the copper pipe ok? The energy you applied to it is being converted to electricity as the magnet is moving slowly through the pipe. But lets say you had the magnet attached to a stick and constantly applied the "push" throughout the pipe. Will it still decelerate? As @Vincent-Lyon.Fr said "will depend on the initial velocity of the magnet, provided no other forces are acting on it." Lets say YES there was another force acting on it! And thats the push from the stick through the pipe.

15. OneOwOne

What would happen then?

16. Vincent-Lyon.Fr

"What would happen then?" Answer : the greater the push, the greater the velocity. There will be a short transitory phase, but if you push with constant force, the force opposed by induction will soon be exactly opposite to the force applied and the magnet will move at constant velocity. It is a terminal velocity similar to that attained by a falling body with air resistance. The greater the weight, the greater the terminal velocity. It is even simpler with the magnet because the magnetic force is proportional to v whereas the air drag is proportional to v².

17. Mashy

drag force is proportional to v too ?? stoke's law says Fd = 6 pi eta a v ? :O anyhoo... like he said.. as you keep pushing more and more.. coil also starts opposing more and more.. ultimately you ll be tired of pushing :P

18. Vincent-Lyon.Fr

Stokes law is only valid at low Reynolds number. A falling body in air (skydiver for instance) is above that threshold; this is the reason why air-drag varies as v².

19. OneOwOne

Even if the coil opposes the magnet, at constant force the magnet will hopefully have a constant speed. @Vincent-Lyon.Fr Could you create an example for this situation? My example: If the initial velocity was 50m/s with a constant force lets say 180N Passing through the coil with the same constant force of 180N the magnet will still have a velocity of 50 m/s? I know its a bad example but I am I heading to the right direction?

20. Vincent-Lyon.Fr

Whatever the initial velocity, the terminal velocity depends only on the force applied. Let's say if you apply 180 N, the velocity will be Vo; then if you apply 360 N, the velocity will be 2Vo. That's as simple as that.

21. OneOwOne

@Vincent-Lyon.Fr Just to be sure. Lets say we applied 180 N of contant force to move the magnet through the coil, the induced current will resist the magnet's force with 180 N so total force is 360N, however, in opposite directions: ---> <--- Input Resisting Force Force from the coil 180N 180N And lets say the initial velocity of the magnet before entering the coil was 100m/s after going through the coil and the constant force of 180 N is still pushing on the magnet. What would the velocity be?(Please solve this problem). In this case, the force is still being applied to push the magnet through the coil, would that force be enough to maintain the speed of 100 m/s? @Mashy