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So let us summarize what we have learned in this lecture about the early electrodynamics, so we have



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learned about double slit experiment, which essentially was the main proof why light must behave as



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a wave.



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But please also remember, there are some experiments which require light having a particle like properties.



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But we will not really focus on these experiments here, these early experiments, which in the end



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gave rise to quantum mechanics.



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And here we want to go one step back and want to consider only the electrodynamics, which is light



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being a wave.



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Furthermore, it was already known that there is a concept of magnetism and of charge and that there



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are some fields related to to charge and to magnets, which are the electric field and the magnetic



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field.



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And also there were already some numerical evidences and some laws describing these concepts here.



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So these this is the Cullum's law, which describes the force between two charges with respect to their



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distance.



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So it's one of our square law.



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Then we have the impasse law, which describes that you generate a magnetic field by currents or by



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moving charges.



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In general, however, we have also learned that here we are missing a term because this violates the



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continuity equation.



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So this was something that one has to keep in mind, but also one has to take care of this missing term.



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And then there were other experiments which explained or which point towards the existence, a concept



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called induction.



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So here we've learned, for example, if you take a wire loop and you put it into a magnetic field back



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and forth, you will generate a voltage.



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So this induction voltage here, so these are all the laws that were essentially known to be true except



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for this missing term.



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And also here we have these different quantities and phenomena that were also known to be true.



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So what Maxwell now did is he took all of these known facts and all of these evidences and concepts



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and put them into four equations.



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And these are the Maxwell equations that we want to discuss in the next section.