2303_-_Spr_2011_-_Week_6_-_Light,_Mirrors,_Lenses

# 2303_-_Spr_2011_-_Week_6_-_Light,_Mirrors,_Lenses - Dipole...

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Dipole radiation pattern Oscillating electric dipole generates e-m radiation that is linearly polarized in the direction of the dipole Radiation pattern is doughnut shaped & outward traveling zero amplitude above and below dipole maximum amplitude in-plane proportional to sin( ϖ t ) UIUC

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Antennas Dipole: Alternating electric field produces an AC current in the circuit. Loop: Alternating magnetic field produces an AC current in the circuit.
Dipole Radiation Plotting the angular distribution:

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Week 6.1 - Reflection Homework Review Reflection Next time Refraction Snell’s Law for Refraction Total Internal Reflection answers.com

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reflecte d ray refracte d ray MATERI AL 1 MATERI AL 2 incide nt ray Geometric How does light travel in real materials? must include dielectric constant κ in Maxwell’s Equations index of refraction, n . Study waves with w << object size. Assume that light propagates in straight lines, called rays . Study the REFLECTION and REFRACTION of these rays at the interface of two materials.
Reflection The angle of incidence equals the angle of reflection θ i = θ r angles measured from the normal reflecte d ray refracte d ray MATERI AL 1 MATERI AL 2 incide nt ray

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Reflection This law is quite general; we discuss the simplest case when surface is a good conductor The electrons on the surface of the meta will experience a force F=eEx acceleration ax → radiation in . e The angle of incidence equals the angle of reflection θ i = θ UIUC First consider a wave impinging on a conductor at normal incidence:
Reflection By superposition, (total field) = (incident field) + (reradiated field) . But we know E tot = 0 inside the conductor . Therefore, inside the conductor . The field created by the surface electrons as they screen the incoming wave completely cancels the incident field inside the conductor, and also is the source of the “reflected” wave. No Ray Reflected Ray Incident Ray

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Reflection Now consider non-normal incidence The components of E parallel to the surface of the incident and reflected waves must cancel for the same reason. θ ι θ ρ x E i θ ι E r θ ρ UIUC
Next Refraction Total internal reflection Reading: Chapter 35.3, 35.5

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Week 6.2 Refraction, Snell’s Law Index of Refraction Refraction Snell’s Law Dispersion Total internal reflection
How does light interact with matter? “Charge on a spring” description of electrons “bound” to atoms in dielectric materials Driven charges re-emit waves that are out of phase with incident wave ϖ ϖ light frequency Light interacts with matter by causing internal charges in the material to oscillate Due to inertia, “bound” charges in a material respond sluggishly to incident light UIUC

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