2 wire with current same direction will attract each other, if wire A is fixed, wire B will move to wire A, work must be done on B by A. Work done = energy , where does this energy of A come from?
The wire A has a current I ,Energy = IVT. Since the I and V no change , the energy in wire A remain the same, then where is the energy required to move B towards A come from?

Question

2 wire with current same direction will attract each other, if wire A is fixed, wire B will move to wire A, work must be done on B by A. Work done = energy , where does this energy of A come from?
The wire A has a current I ,Energy = IVT. Since the I and V no change , the energy in wire A remain the same, then where is the energy required to move B towards A come from?

jt950 · Answer

Some expert please explain

fifciol · Answer

the flowing of charges (current) causes magnetic field. When wire be with some current flowing is in that magnetic field it will feel the force pointing towards the fixed wire( when the signs of current are in the same direction) So the energy comes from the magnetic field from both wires that is producing all the time while the currents are flowing

jt950 · Answer

magnetic field energy come from current?

fifciol · Answer

yes

jt950 · Answer

how to count that energy?

fifciol · Answer

force of attracting times the displacement it's only the kinetic energy that you can get out of these wires

jt950 · Answer

when the magnetic field energy is used to attracting the wire B , the current will decrease(due to energy lose)?
or current remain?
If current remain that's mean i have infinity magnetic potential energy?

jt950 · Answer

If current remain that's mean it have infinity magnetic potential energy (for correction)

fifciol · Answer

it's hard to predict if current remains the same due to changing magnetic field during the motion, but it remains the same due to power supply

jt950 · Answer

i have the only question - where is the energy of magnetic field come from? current?
If it's from current, then the power supply E=IVT , the current remain the same mean the energy in current remain the same E=IVT. 
The problem come , magnetic field need to do work on wire B, it required energy , since it's energy is from current but the energy in current does not drop on same power supply?So no energy is draw from current(By magnetic field)?

fifciol · Answer

the magnetic field increases as the wire moves towards fixed one and so the force, that's why the energy increases