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Lenz's law and elctromagnetic waves

  1. Apr 4, 2013 #1

    We're just starting to learn about electromagnetism and electromagnetic waves. I am still trying to grasp all these new concepts, but there's a question that's bugging me.

    From what I understood an alternating magnetic field will generate an alternating electric field which in turn will generate a magnetic field and according to Lenz's law the direction of this magnetic field will oppose the change in flux in the original magnetic field. Today in class, my teacher explained that an electromagnetic wave is produced by an alternating magnetic field that generates an alternating electric field and so on without end.

    My question is: How can these fields generate continuously without end? Doesn't Lenz's apply to these waves? (as it states that generated magnetic field will oppose the change in magnetic flux and so these fields won't generate without end).

    Did I just get it all wrong?:confused:

    Help appreciated!!!
  2. jcsd
  3. Apr 4, 2013 #2
  4. Apr 4, 2013 #3
    The thing you described in your OP post is actually how the earth's dynamo works , only in earth the magnetic field is produced due to the flow of hot lava inside the core and lava is a conducting fluid.


    And everything is fine here as long as conservation is in mind because the em field can only go as far as the input energy and everything in it's way allows it to go.
    Now you have current going through a wire let's call it a radio transmitter in this case electric field with a certain frequency creates a magnetic field with a certain frequency now that magnetic field goes and sees antennas , cars , buildings, trees and air also in it's way and induces a current in each of them , ofcourse the energy is so low that you won't notice that if only in your radio receiver but the energy get's wasted in many different object in it's way.
    Remember microwave oven is nothing more than a sort of radio transmitter aimed for very short distance objects , everything that has something conducting inside like water in food or water in trees will heat up as it has received some amount of energy.

    Theoretically if you would have perfect lossless transformers tied in series one after another and if you would put constant input energy you would get the same energy out after infinite amount of transformers in series as the only way that wastes and em wave is interaction with the surrounding and material loss from the device in which it originates itself.
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