From: PointedEars@web.de   
      
   Kuan Peng wrote:   
   > Le 20/01/2026 à 17:11, Thomas 'PointedEars' Lahn a écrit :   
   >> There is; it is called Lenz's Law:   
   >   
   > If at the beginning the current in A is constant,   
      
   What exactly do you mean by that?   
      
   > do you think that there is a current in the coil B?   
      
   Unless coil B is in the vicinity of a voltage source, or if the external   
   electric field is not constant, then there should not be:   
      
     ∇ × E = −∂B∕∂t,   
     ∇ × B = μ₀ J + (1/c²) ∂E∕∂t   
      
   and   
      
     J = σ E,   
      
   where σ is conductivity, and   
      
     I = ∬ dA ⋅ J,   
      
   so there is a current when the magnetic field changes, or there is a   
   non-zero electric field (that is produced by the voltage source).   
      
   But one has to be careful here.  A *measured* current is rarely exactly 0   
   all the time; for example, there is interference from external source, and   
   the phenomenon and practical problem of a /Kriechstrom/ (literally: crawling   
   current).  Experimental evidence that a measured current is not zero is   
   therefore insufficient to confirm the claim that Faraday's law of induction   
   would be wrong or needed refinement.  Much of it depends on your   
   experimental setup.   
      
   --   
   PointedEars   
      
   Twitter: @PointedEars2   
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