Quote:
Originally Posted by ARPAN  u r on ur way, bottomlander.
question 3.
hold a magnet fixed and keep bringing an iron bar towards it.
We observe that the iron bar gets attracted towards the magnet everytime it is kept within a certain range of the magnet... from where does this energy come i.e. who does the work and on whom the work is done...THINK!!
let us assume that this energy is obtained from either the magnet or iron internal energy.. And if this were so then after repeating the experiment for a good number of times the magnet would lose its magnetism or the iron after losing all its energy would no longer be attracted towards the magnet. but in practice neither of the things happen.WHY ????
we know (although without any proof but basically by extensive experiments performed by our scientists) that energy can neither be created nor be destroyed..ALSO THINK ABOUT THE SOURCE OF THE ENERGY BY VIRTUE OF WHICH IRON GETS ATTRACTED....OR ARE WE HEADING TOWARDS CONSTRUCTION OF A PERPETUAL MACHINE...
one common misconception is that the iron might have got magnetised during the course of the experiment. to get a clear picture u can consider taking different pieces of iron bar each time yet arriving at the same result..
u can use the concept of magnetic domains if necessary... |
I am thinking about the contribution from potential energy.
I prefer an analogy of gravitational field rather than an electric field (seems that magnetic fields cannot be shielded).
Static electric field can be shielded with an hollow metallic sphere, but magnetic field can't (only can be neutralized under opposite polarization).
It looks like a PERPETUAL DEVICE only when the additional work of moving out the iron bar (restore the potential energy) hasn't been taken into account.
Work/power is required for the removal of the old iron bar because magnetic field cannot be shielded.
Just a wild guess because I forget much of my knowledge in physics course already.
Best Regards. Bottomlander