Lecture 23 Lecture Notes

# Lecture 23 Lecture Notes - of dipole moment Full Dipole...

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7.5 Electric Dipole Radiation 7.5.1 Electric Dipole Approximation In this approximation we find 7.4.2 Multipole Expansion 7.4.2.1 Reminder: Multipole Expansion in Magnetostatics multipole expansion for fields sufficiently far from the source area magn. monopole magn. dipole magn. quadrupole 7.4.2.2 Multipole Expansion in Electrodynamics multipole expansion for fields sufficiently far from the source area leading order => electric dipole approximation Approximation to leading order leads to the electric dipole radiation, (as we will see) Lec 23 - 6. Mar January 29 08 9:54 PM Lecture Notes Page 1

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Here we used the following two observations continuity equation side calculation (integration by parts) apply to both sides with area G including all sources outside source area J=0 apply with spectral density

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Unformatted text preview: of dipole moment Full Dipole moment: Def Lecture Notes Page 2 7.5.2 Electric & Magnetic Field Components 7.5.2.1 Magnetic field: define Aside: in spherical coordinates constant 7.5.2.2 Electric field Outside source area: Observation: transverse (orthogonal to ), but is not transverse! 7.5.3 Near field and still assume r much larger than source dimensions so dipole approximation valid! Amplitude of smaller than that of Observations: 1) Lecture Notes Page 3 Amplitude of smaller than that of dominates Observations: 1) 2) is basically static dipole field in this approximation (compare Griffith Eqn. 3.104) 7.5.4 Far field (Radiation Zone) Observations: 1) and transverse (orthogonal to ) 2) Comparable amplitudes for and . Lecture Notes Page 4...
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## This note was uploaded on 07/28/2009 for the course PHYS 441B taught by Professor Norbertlutkenhaus during the Winter '09 term at Waterloo.

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Lecture 23 Lecture Notes - of dipole moment Full Dipole...

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