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52                       Schro Èdinger wave mechanics
                              ψ 1                                       |ψ | 2
                                                                         1

                                                         x
                                 0                      a                   0                      a




                              ψ 2                                       |ψ | 2
                                                                         2

                                                         x
                                 0                      a                   0                      a




                             ψ 3                                      |ψ 3 | 2


                                                        x
                                0                      a                   0                     a





                             ψ 4                                      |ψ | 2
                                                                        4

                                                         x
                                0                       a                  0                      a



                                                                               2
                             Figure 2.2 Wave functions ø i and probability densities jø i j for a particle in a one-
                             dimensional box of length a.



                             said to be orthonormal. The orthogonal property of wave functions in quantum
                             mechanics is discussed in a more general context in Section 3.3.
                               The stationary states Ø(x, t) for the particle in a one-dimensional box are
                             given by substitution of equations (2.39) and (2.40) into (2.31),
                                                        r  
                                                           2     nðx   ÿi(n ð "=2ma )t
                                                                                 2
                                                                          2 2
                                               Ø(x, t) ˆ    sin       e                        (2:44)
                                                           a      a
                             The most general solution (2.33) is, then,
                                                     r  
                                                        2  X        nðx   ÿi(n ð "=2ma )t
                                                                                    2
                                                                             2 2
                                            Ø(x, t) ˆ        c n sin     e                     (2:45)
                                                        a            a
                                                           n
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