228s13-l04

For radio with mhz ghz frequencies this can be done

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Unformatted text preview: , ±2, ... For minima, we want destructive interference: r2 - r1 = (m+½)λ, with m = 0, ±1, ±2, ... For water, it is pretty easy to keep the two sources in phase - you drop two small stones at the same time. For radio, with MHz - GHz frequencies, this can be done electronically. But for visible light, with f ≈ 1015 Hz, this is difficult. How do we get around this? Sunday, February 24, 2013 In-phase light sources - Old Technique How do we get around this? We cheat. We take a coherent LASER source and divide it into two. What do we see from the interference of the two inphase light sources? Diffraction - more about this in two lectures. Sunday, February 24, 2013 Two in-phase light sources. In-phase light sources Standard geometrical approximations for analysis: 0) variations in path length over width of band or slit << wavelength 1) the two slits are narrow compared to their separation 2) The distance to the screen is large compared to the slit separation. Sunday, February 24, 2013 Geometry and Algebra Since the path difference is dsinθ, and we get maxima when the difference is an integral number of wavelengths, when mλ = dsinθ or sinθ = mλ/d. The vertical positions of the bands on the screen become y = Rtanθ ≈ Rsinθ = mRλ/d. Sunday, February 24, 2013 In-phase light sources To the left: a picture of alternating light & dark bands. maxima at y ≈ mRλ/d. minima at y ≈ (m+½)Rλ/d. Sunday, Fe...
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This document was uploaded on 02/18/2014 for the course PHYS 228 at Rutgers.

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