Thermionic emission

The work function W of a metal is the minimum energy required to enable an electron to escape from its surface.         

Measurement of e/m by J. J. Thomson's method  :

           and  e E = e v B

The cathode-ray oscilloscope ( CRO )  : 

Measurement of phase relationships     : 

Suppose       x = x_o sin wt             

                    y = y_o sin ( wt +  )

Comparison of frequencies     :     Lissajous figures