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Why is del(E_t) zero in TEM mode of transmission lines?

  1. Jul 9, 2017 #1
    I was going through MIT opencourseware https://ocw.mit.edu/courses/electri...s-spring-2009/readings/MIT6_013S09_chap07.pdf and I didnt understand exactly why in equation 7.1.37 and 7.1.38 in page 192 the divergence of transverse electric field is taken as zero ? The only reason this would be true is if the region is source free but we clearly see that this field does setup a surface charge density on the surface of the transmission line so intuitively and mathematically why would the divergence of Et be zero? I can always construct a surface in the transverse plane to include the transmission line which has charge and so the del.Et should be equal to the surface charge density isn't?
  2. jcsd
  3. Jul 9, 2017 #2
    The divergence of E is zero in between the conductors because there is no charge in that space. The surface charge density is only used for boundary conditions when solving for the fields.
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