Chapter3_19

Chapter3_19 - = hf – W and e W f e h V c − = ∆ Now...

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PHY3063 R. D. Field Department of Physics Chapter3_19.doc University of Florida The Photoelectric Effect (2) The energy E = KE + U of one electron at the photocathode and at the collector is given by 2 2 2 2 2 1 1 1 1 1 eV KE qV KE E eV KE qV KE E = + = = + = , where q = -e. Energy conservation implies V e KE KE = 2 1 , where V = V 1 – V 2 . If e V > KE 1 then no electrons reach the collector. Let V c be the “critical” potential where electrons first start reaching the collector ( i.e. KE 2 = 0). Hence e V c = KE 1
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Unformatted text preview: = hf – W and e W f e h V c − = ∆ . Now plot ∆ V c versus the frequency, f , of the incident light. Determine h from the slope of the line. Get s eV s J h ⋅ × = ⋅ × = − − 15 34 10 136 . 4 10 626 . 6 . Action: Note that 2 X f E = has dimensions of “action” . V 1 V 2 electrons Incident Light photocathode collector frequency f ∆ V c-W/e Slope = h/e Same h that Planck found! “Action”!...
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