HMWK 4 - KEY.pdf

# HMWK 4 - KEY.pdf - HOMEWORK 4 Due Friday 2 March 1 A photon...

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HOMEWORK 4 Due Friday 2 March 1. A photon with = 305 nm ejects an electron from a metal. The kinetic energy (E k ) is measured to be 1.77 eV. a. Calculate the threshold for photo-ejection (i.e. the work function) for this metal in units of eV (1 eV = 1.602 × 10 19 J.) and as a frequency 0 For the photoelectric effect: ℎ𝑐 𝜆 = 𝐸 𝑘 + ? ; ? = ℎ𝑣 ? W = workfunction of metal ℎ? 𝜆 = 𝐸 𝑘 + ? ; ? = ℎ𝑣 ? 6.63 × 10 −34 𝑘𝑔? 2 ? −1 3 × 10 8 ? ? 305 × 10 −9 ? = 1.77(1.6 × 10 −19 𝐽) + ? ; ? = ℎ𝑣 ? ? = (6.52 × 10 −19 𝐽 − 2.83 × 10 −19 𝐽) = 3.69 × 10 −19 𝐽 = 2.3 ?? ; 𝑎?? 𝑣 ? = 5.6 × 10 14 𝐻𝑧 (??? ??????, ?? 1 ? ) b. Assuming a pure metal, and not an alloy, what metal(s) could this be? b. Wikipedia gives a list of metals…..those with W ~ 2.3eV - most likely K, but within experimental error, could also be: Na, Rb c. What is the momentum of the ejected electron? c. 𝐸 𝑘 = 1 2 ? 𝑣 2 = ? 2 2? 𝑎?? ? = √2?𝐸 𝑘 ? = ????(2 ∗ 9.1 × 10 −31 𝑘𝑔 ∗ 2.83 × 10 −19 𝐽) = 7.18 × 10 −25 𝑘𝑔 ? ? This is an electron with velocity, v = p/m = 7.9x10 5 m/s, BTW!

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