1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Infinitel potential well

  1. Jun 8, 2014 #1
    three parts to this one, I cant seem to justify my values, units cancel, but the numbers don't seem right. I think I may have used a wrong equation for part B but I don't know what else to use.

    Problem: An electron is confined to an infinitely deep potential well of width 0.120 nm.
    a.) Calculate its ground state energy, E1
    b.)If the electron makes a transition from the n=3 state to the n=2 state, how much energy is carried away by the emitted photon?
    c.)What is the wavelength of this photon?


    a.) [tex]E_1 = \frac{pi^2 (hbar c)^2}{2M_e C^2 a^2}[/tex]

    b.) [tex]E_\gamma = E_3 - E_2[/tex]

    c.) [tex]\lambda = \frac{hc}{E_\lambda}[/tex]

    My attempt:

    a.) using hbar*c = 197 ev*nm and MeC^2 = 511000 ev i get a value of 26.02ev for E1

    b.) using the same equation as above for the n=3 and n=2 states and subtracting I get 130.13ev

    c.) using hc = 1240 ev*nm I get an answer of 9.53 nm which doesn't seem right to me. I feel like the photon should have a larger wavelength.
  2. jcsd
  3. Jun 8, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Why do you think the photon should have a bigger wavelength?

    Lets see - using ##h= 2\pi \hbar## ;$$E_n=\frac{n^2(h c)^2}{8mc^2a^2}=n^2E_1$$ (when you use LaTeX, put a backslash in front of the symbol name so \hbar renders as ##\hbar## etc.)

    hc=1239.8 eV.nm
    mc^2=511000 eV

    Looks good to me:
    Go through the arithmetic one step at a time, make sure you have squared the correct terms.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted