TEST1_ENSC3313_SP2006_KEY

# TEST1_ENSC3313_SP2006_KEY - ENSC 3313 Spring 2006 TEST 1...

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1 ENSC 3313, Spring 2006 TEST 1 - KEY Name_________________________ Answer all 10 questions, show all work, 2points each 1. A glow-in-the-dark Eskimo Joe's cup is made by adding zinc-sulfide phosphor to the polyethylene plastic. After "charging" the cup by placing it in sunlight, the glow-in-the-dark light intensity decreases by 90% after only ten minutes. This is exponential decay, calculate the decay constant (in minutes) for the zinc-sulfide phosphor. Exponential decay formula = τ t o e I I After 10 min, 10% remains so: () 1 0 10 10 1 0 1 0 10 . ln . ln e . I I o = = = = The decay constant is: min . 34 4 = 2. Many motion detectors (such as those that open the doors at Wal-Mart) sense infrared (heat) radiation when people enter the field of vision by a property known as pyroelectricity. If the radiation to be sensed has a wavelength of 10 micrometers, what is the energy of these photons in eV? Note: speed of light c=3 × 10 8 m/s, Planck's constant h=6.626 × 10 -34 J s, 1 eV = 1.6 × 10 -19 J The energy of a photon is: ν h E = , and the frequency is: λ c = For IR at 10 micron: 1 13 5 8 10 3 10 10 3 × = × = s and ( )( ) ( ) eV . . / . E 124 0 10 6 1 10 3 10 626 6 19 13 34 = × × × = FYI: Only crystals that don't have a center of symmetry can be pyroelectric.

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## This note was uploaded on 01/10/2012 for the course ENSC 3313 taught by Professor Staff during the Fall '11 term at Oklahoma State.

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TEST1_ENSC3313_SP2006_KEY - ENSC 3313 Spring 2006 TEST 1...

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