m is the mass of one ferromagnetic material which was equated from two possible masses m1,m2 into one. The Magnetic potential,M has been defined by the energy per pole of magnetic flux per unit in the magnetic H field. The flux phi can be derived as the mass drawn into that measured H field bot…tlfong013807Oh my goodness, I though EE75’s answer is concise and should be good. So I read the first sentence, and so far so good. Then big trouble came when I read the second sentence. I know what is electrical potential, but what the hack is “magnetic potential”? Yes, it defined by “energy per pole” of “magnetic flux per unit” of “magnetic field”, all of which are Greek to me, no wonder denoted by Greek symbols Anyway, I dared not to read the third sentence when I sneak previewed the term “mass” which I guess is what the OP is asking about. Another scary term is “gap”, again, what the hack is it?Yesterday I bought a RFID reader and the spec says it is only near field NFC, not far field. But I want to detect the RFID tag farther. So I googled and read that NFC is mainly Electrical field, very little Magnetic field. I was surprised, because I always (wrongly) thought that E & M always go together. My conclusion is that I know too little magnetism to properly use the RFID reader. . I googled and found the book the OP is reading and started reading Chapter 6. / to continue in my answer below.. Tony Stewart Sunnyskyguy EE75They always go together but the mutual impedance is sqrt[L/C] and the RFID uses both to send and receive with different source impedances to load. Geometry and gaps play a big role in mutual inductance and capacitive coupling of E fields. A scope probe picks up 50/60 Hz E fields from your finger while an arc nearby from a current transient can couple into a shorted probe loop in the RF spike. tlfong013807Thank your for your explanation. So I now understand that E and M waves/field do always go/exist together. It is only the probe/antenna that prefers to read/pick either E or M, or more E, less M, or vice versa etc.By the way, your saying of geometry and gaps reminds me of my experience of my tech collage days when I DIY AC200 to AC12V transformers. I went to a scrap metal shop and bought 2 catties of E shape and I shape iron plates, and placed one plate on top of the other, interlacing the E directions, leaving little gaps (not sure) of the assembled core, preventing eddy current..At that time, I know that the gap is to prevent the eddy current flowing inside the “core”. I was happy some years ago when I bought my first induction cooker and realized that if there is no gap, therefore eddy current flows freely and heats up the metal pot above the cooking surface, and boils my egg. I also now realize that some rice cookers use induction current to heat up the rice grains very evenly, because they using induction current to evenly heat up the rice pot side walls, not just the bottom part of the pot. Cheers. Tony Stewart Sunnyskyguy EE75sometimes there are too many false assumptions in your statements to correct. These ought to go in the chat room. Eddy Currents only occur in your thicker laminates not the thinner insulation tlfong013807Ah, I very much agree. Actually I was hesitating to say that I actually knows or remember very little about gap, except that gap should increase flux flowing through the core. I know when I studied my EED diploma, my classmates taking the “heavy current” should know many times more heavy current stuff. Abut the eddy current and induction cooker thing, / to continue, … Tony Stewart Sunnyskyguy EE756:36Induction cooking only works on metal bases not water or oil based ingredients. tlfong013807I confess I have not googled or wiki enough about induction cooker so my guess are very likely just wishful thing, just a reflection of what EE stufff I learnt in college can apply in daily lives of induction cooker and microwave oven. I suggest we take a break, and let me studied more before I ask you again for help. BTW, your advice on three phase electricity distribution is very useful to my knowledge in smart city projects. / to continue, …I recently joined a community project on home solar energy and found that my knowledge in home solar energy and how to join it to the grid is almost zero. So I need to also study more before I ask questions again in EE SE. Just thinking aloud. Sorry for all the typo errors. About induction cooker – yes I know it only works for “magnetic” metal pot. Sorry if I have mislead you about water or oil. Cheers. Tony Stewart Sunnyskyguy EE75It’s others you could be misleading tlfong013807Ah, I am sorry if I misled others about water and oil with induction cooker. I did not recall anything about this part. Let me see if I can go back to search about oil and water. Many thanks for pointing that out. I always feel sorry that others think that I know a lot about computer and EE and do not try to point out my mistakes, even if they are very sure. Once I was a computer teacher and I always told me students that things go too fast and I could not catch up fast enough to teach, I knew mainframe computer, but mini came along, and then microprocessor, then mcu, then .OMG, Bed time.. The last message was posted 5 hours ago.