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exam3-sol

Showyouequationscf3x10812x101525x107m250nm 9

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Unformatted text preview: tion produced? Show calculation. T=1/3 sec so f=1/T=3 Hz 6. In what part of the E‐M spectrum is the radiation in problem #5? Very long wavelength radio waves. 7. The work function ф is the amount of energy it takes to pry an electron from a metal. For copper ф = 4.5 eV. What is the lowest frequency light which can free an electron from copper? E=фq=4.5x1.6x10‐19 Joules and f=E/h so f=4.5x1.6x10‐19 /6.2x10‐34 = 1.2x1015 Hz 8. What is the wavelength of the photon in problem #7? Show you equations. λ=c/f=3x108/1.2x1015=2.5x10‐7 m=250nm 9. What part of the E‐M spectrum is the photon in problem #7? Show your logic in case you got #7 wrong. UV 10. What is the momentum p (in Kg m/s) of the photon in problem #7? Show your logic in case you got #7 wrong. Hint: If you use one system of units (m, s, Coulombs, Hz) it will come out correctly.p=E/c=hf/c=h/λ=6.2x10‐34/2.5x10‐7=2.5x10‐27kg‐m/s2 11. How does the product of the answer for #8 and #10 compare to what you expect for ΔxΔp from the uncertainty principle? λp=2.5x10‐7 x 2.5x10‐27= 6.2x10‐34 which is h (Planck’s constant) as it should be! (within a factor of 2 or so). 12. What physical property does not change when...
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