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).