Fig. 2-8. The first six probability amplitudes y>n>(x) for an electron moving on a line of length L. Note the y>n>(x) may be negative in sign for certain values of x. The y>n>(x) are squared to obtain the probability distrubrition functions P>n>(x), which are, therefore, positive for all values of x. Wherever y>n>(x) crosses the x-axis and changes sign, a node appears in the corresponding P>n>(x).