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Physics 6C Final Practice Solutions

# Physics 6C Final Practice Solutions - Physics 6C Final...

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Physics 6C Final Practice Solutions Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB

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Use the following information for problems 1 and 2. A beam of white light with frequency between 4.00 x 10 14 Hz and 7.90 x 10 14 Hz is incident on a sodium surface, which has a work function of 2.28 eV. 1) What is the range of frequencies in this beam of light for which electrons are ejected from the sodium surface? An easy way to do this one is to find the frequency of a photon that has an energy of 2.28 eV. Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB Hz 10 5 . 5 f ) f ( ) s eV 10 14 . 4 ( eV 28 . 2 f h E 14 15 photon Now we just have to realize that any photon with a higher frequency will have more energy, and will also eject electrons. So the answer is (d).
Use the following information for problems 1 and 2. A beam of white light with frequency between 4.00 x 10 14 Hz and 7.90 x 10 14 Hz is incident on a sodium surface, which has a work function of 2.28 eV. 2) What is the maximum kinetic energy of the photoelectrons that are ejected from this surface? We use the most energetic photon available the one with the highest frequency. Its energy will be higher than the work function, and the difference will be the leftover KE. Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB eV 99 . 0 KE eV 28 . 2 ) Hz 10 9 . 7 ( ) s eV 10 14 . 4 ( KE f h KE max 14 15 max max Convert to Joules: J 10 6 . 1 ) 10 6 . 1 ( ) eV 99 . 0 ( KE 19 eV J 19 max Answer (b)

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3) When light of a particular wavelength and intensity shines on the surface of a given metal, no electrons are ejected. Which of the following changes will most likely cause the emission of photoelectrons? a) Decreasing the frequency of the light b) Increasing the intensity of the light c) Decreasing the wavelength of the light d) Increasing the wavelength of the light In order for electrons to be ejected, the photons have to have more energy. To do this we need to either increase the frequency or decrease the wavelength. Changing the intensity will not change the energy of individual photons. Answer (c). Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB
4) What is the De Broglie wavelength for a Helium atom (atomic mass=4.002603 u) traveling at a speed of 10 3 m/s? Use the conversion factor 1 u = 1.66054 x 10 -27 kg. This one is just a formula: Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB m 10 0 . 1 ) 10 ( ) 10 66054 . 1 ( ) u 002603 . 4 ( s J 10 63 . 6 v m h 10 s m 3 u kg 27 34 Answer (b). You may have to round up carefully on this one.

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5) The position of an electron is measured to within +/- 10 -6 m. What is the minimum uncertainty in the electron’s velocity? Use electron mass = 9.11x10 -31 kg.
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Physics 6C Final Practice Solutions - Physics 6C Final...

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