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Homework Help: Particle in a box, some clarification please

  1. Dec 8, 2013 #1
    the energy of an n state can be given by:

    E = (nh)^2 / 8mL^2

    is this a representation of the Kinetic energy of the particle? i thought it was but this question has got me confused.

    it asks for the Energy of the n=1 state, which ive done. then it asks what quantum number, n would be needed if the Kinetic Energy was 0.025eV.

    i rearranged the above eqn for n and put E= (0.025ev X 1.6x10^-19 ), but get something stupid as a result.

    so, is E the energy of the state of the particle OR it's kinetic energy OR both?

    Thanks in advance for any help.
  2. jcsd
  3. Dec 8, 2013 #2
    Hmm, the energy state is the total energy, but as you only have kinetic energy, it should be straight forward, as you've done.
  4. Dec 8, 2013 #3


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    Gold Member

    The potential in the case of particle in a box problem,is zero inside the box and greater than zero outside it.So inside the box,the total energy of the particle is equal to its kinetic energy.
  5. Dec 8, 2013 #4
    yes this is as i suspected, i get a stupidly high number for n and its not a whole number either! will recalculate.

    thanks for the replies!!
  6. Dec 8, 2013 #5
    Well, getting a whole number for n is quite unrealistic, when you think about the numbers and decimals, you are using.

    Also I don't think there are any limits for the quantum number for a particle in a box.
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