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Homework Help: A few questions on quantum mechanic and photoelectric effects

  1. Oct 12, 2013 #1
    Hi all,

    I have a total of 6 questions, 3 of them are posted here and 3 of them are provided in the link because they involve graphs.

    1. KE of an electron is twice that of a proton, what is ratio of de broglie wavelength of proton:electron?
    My answer: since de broglie wavelength is lamba = h/mu. I put in all the values and mass of electron and proton. In the end, I get the answer as 0.00109. But I wish someone can help me double check to see if my answer is correct.

    2. If given work function of a metal, eg 2 Joules. And given wavelength of a photon to be eg, 5 meter. how to find stopping voltage? In another word, if given wavelength (in meter) and work function (in Joules), how to find stopping voltage (in Volt)?
    My answer: I am unsure of this question because I am unsure about the relationship between wavelength, stopping voltage and work function. Is it c/hλ + work function = stopping voltage?

    3. A spherical molecule has mass "M" kg and diameter of "D"nm. The uncertainty in position is equal to the diameter. What is the minimum speed of the molecule?
    My answer: This question I don't really know. I think it involves heinsberge uncertainty principle. Anyone can enlighten me?

    4. http://i42.tinypic.com/2pzmq38.png
    My answer: My educated guess is option B because since both source one and two have same wavelength, starting applied voltage should be same. But I do not understand why graph of source II is higher than graph of source I. Please tell me if my answer is correct or wrong and explain your answer in detail.

    5. http://i44.tinypic.com/214pi61.png
    My answer: My guess is option 4. It is related to question 4. If someone can explain question 4, i think i can do this question. Please tell me if I am wrong or correct, and why.

    6. http://i42.tinypic.com/ka4j8k.png
    My answer: This question i really have no idea. Someone please help me ):

    For all questions, please provide an answer and tell me why you think it is the answer. Explanation is key.

    Thank you for your time!
  2. jcsd
  3. Oct 12, 2013 #2


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  4. Oct 12, 2013 #3
    momentum = mass multiple velocity..

    so i just break it up? Did i do it wrongly? =.=
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