MSE2020LectureNotes_1_18 - U = energy density ∝ U A2 For...

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MSE 2020 1/18/2011 Page 1 of 2 Alamgir’s Cell Number: 201-240-9367 – call anytime before 10pm with questions Presentations: 15 min presentation (15 min = 15 slides or less, approximately 1 min/slide) 5 min Q&A (asking questions is part of participation grade) Use any resources, just double check (2+ sources) One slide must be a resource list Divide presentation into: o Source o Unique features you can measure o Sample preparation o Environment sample is measure in o Does the tool measure surface or into bulk (how far into sample – depth of view?) o Detection Geometry Kind of detectors o How is it constrained/limited? o What makes this technique unique? Describing Light A = amplitude K = wave number φ = phase shift ω = frequency = ( + A cos Kx + ) φ ωt general representation of a wave in motion For light waves, the electric and magnetic fields are oscillating perpendicular to each other. = + E cosKx + ωt φ Electric field
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MSE 2020 1/18/2011 Page 2 of 2 = + B cosKx + + ωt π2 φ Magnetic field Treat the electric and magnetic fields like vectors for addition and subtraction.
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Unformatted text preview: U = energy density ∝ U A2 For mechanical waves An historical experiment measured KE of electrons emitted from Na metal due to light. The light’s intensity and frequency was varied (Einstein’s Photoelectric Effect experiment). A relationship existed between the energy of the electrons and the frequency of the light, but there was no relationship between the intensity of the light and the energy of the electrons. There is a minimum frequency below which no electrons will be emitted, regardless of intensity. v = frequency λ = wavelength ∝ E v = = E hv hcλ T = period = → = Kλ 2π λ 2πK = → = ωT 2π T 2πω Increasing intensity increased the electric current in the detector (amount of electrons being detected), but it didn’t change the energy of the emitted electrons. The minimum amount of energy needed to knock an electron off is called the work function....
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