(*Several wave functions for the particle in a square box of side  L .  
          Integers  nx and ny are the quantum numbers*) 
L = 10. 
nx = 1
ny = 1
ContourPlot[
      Sin[((nx π x)/L)] Sin[((ny π y)/L)], {x, 0, 10}, {y, 0, 
        10}, PlotPoints -> 25]
nx = 1
ny = 2
ContourPlot[
      Sin[((nx π x)/L)] Sin[((ny π y)/L)], {x, 0, 10}, {y, 0, 
        10}, PlotPoints -> 25]
nx = 2
ny = 1
ContourPlot[
      Sin[((nx π x)/L)] Sin[((ny π y)/L)], {x, 0, 10}, {y, 0, 
        10}, PlotPoints -> 25]
nx = 2
ny = 2
ContourPlot[
      Sin[((nx π x)/L)] Sin[((ny π y)/L)], {x, 0, 10}, {y, 0, 
        10}, PlotPoints -> 25]
nx = 4
ny = 4
ContourPlot[
      Sin[((nx π x)/L)] Sin[((ny π y)/L)], {x, 0, 10}, {y, 0, 
        10}, PlotPoints -> 50]