Module 3 : MAGNETIC FIELD
Lecture 20 : Magnetism in Matter
 
  We can see that $\vec E, \vec B$ and $\vec k$ form a mutually orthogonal triad. The electric field and the magnetic field are perpendicular to each other and they are both perpendicular to the direction of propagation.
  Generation of Electromagnetic Waves
  We have looked for solutions to Maxwell's equations in free space which does not have any charge or current source. In the presence of sources, the solutions become complicated. If $\rho$ = constant, i.e. if $\vec J =0$, we only have a steady electric field. If $\rho$ varies uniformly with time, we have steady currents which gives us both a steady electric field as well as a magnetic field. Clearly, time varying electric and magnetic fields may be generated if the current varies with time, i.e., if the charges accelerate. Hertz confirmed the existence of electromagnetic waves in 1888 using these principles. A schematic diagram of Hertz's set up is shown in the figure.

 
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