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Homework Help: Help with some Quantum physics please

  1. Dec 10, 2007 #1
    I'm in Quantum right now and I'm having lots of trouble with some homework...Any help would be appreciated. If you guys could show how it's done, it would be very helpful.

    1. If the Earth (of radius R = 6370 km) absorbed all photons incident on it from the Sun, what magnitude of force would the solar radiation exert on the Earth? Assume the effective wavelength of solar radiation is 550 nm and the solar luminosity is 3.64 x 1026 W.
    ______ N

    2. An atom represents a region about 2.6 10-10 m wide in which an electron is confined. Use the Heisenberg uncertainty principle to estimate the minimum kinetic energy of the electron, expressing your result in electron-volts (eV).
    ______ eV (model the atom as a one dimensional entity)
    ______ eV (model the atom as a three dimensional entity)

    3. The lifetime of a certain atom while it exists in an excited state before making a transition to a lower-energy state is about 1.2 ns. The wavelength emitted in the transition is 250 nm.

    (a) What is the frequency of the light?

    (b) About how well can the frequency of the light be known?

    (c) About how well can the wave packet (photon) be localized in space?

    4. Certain atoms have special excited states (called metastable states) in which an electron can exist for relatively long times, on the order of 1.1 10-4 s. What is the minimum uncertainty associated with the frequency from such metastable excited states? Such relatively long-lived states make lasers possible; lasers emit light with a very precise frequency.
    ____ kHz

    5. An archeological dig in the basement of a physics laboratory uncovers the bones of a college student who expired some time ago. A careful analysis of the remains indicates a carbon 14 activity of 0.18 Bq per gram of carbon. A freshly sacrificed student has a carbon 14 activity of 0.27 Bq per gram of carbon. The half-life of carbon 14 is 5.73 103 y.

    (c) What will be the activity per gram of carbon of the old student bones when the class of a.d. 6171 graduates?

    Thanks! :)
  2. jcsd
  3. Dec 10, 2007 #2


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    Homework Helper

    You forgot to state some information, like what you've already tried / thought about and what subjects you're currently covering (probably there is a formula giving the answer to a directly, but I suppose you would want us to derive the answer from the stuff you have learned so far).
  4. Dec 10, 2007 #3
    Seriously. So you're saying, "Please give me the answer, and if you could provide the whole solution to boot, that would be great."

    You'll get no help unless you show what you've tried to do, ie, made an effort on your own first. We're not going to do your hw for you. Like the previous poster said, do you have an idea what equation(s) may apply for #1?

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