sol-mt1 - Physics 137A Fall 2009 Midterm#1 Wed Oct 7 th ¯...

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Unformatted text preview: Physics 137A Fall 2009 Midterm #1 Wed. Oct. 7 th ¯ h = 1 . 055 × 10 − 34 Js c = 2 . 998 × 10 8 m/s e = 1 . 602 × 10 − 19 C ǫ = 8 . 85 × 10 − 12 C 2 /Jm m e = 9 . 11 × 10 − 31 Kg m p = 1 . 67 × 10 − 27 Kg ≃ m n 1. (25 points) Answer the following questions succintly: (a) Describe Stefan’s law and Wien’s displacement law of blackbody radiation. Stefan’s Law: The total radiant intensity over all wavelengths increases as the fourth power of the temperature: R tot ≡ integraldisplay ∞ R ( λ,T ) dλ = σT 4 . Wien’s displacement law: The wavelength λ max at which the curve R ( λ,T ) versus λ has a peak de- creases as we raise the temperature as λ max ∝ 1 /T . Numerically, λ max T ≃ 2 . 898 × 10 − 3 m . K , which for T = 300 K yields a peak in the IR. Hence hotter objects glow whiter. (b) Sketch the curve of the photoelectric current versus the potential difference between the electrodes in Lenard’s photoelectric effect experiment, when the cathode is illuminated with monochromatic UV light, for two values of the light intensity. Which feature of the data defies a classical explanation?...
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This note was uploaded on 11/21/2010 for the course PHYSICS 137A taught by Professor Moore during the Fall '07 term at Berkeley.

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sol-mt1 - Physics 137A Fall 2009 Midterm#1 Wed Oct 7 th ¯...

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