The value of e/m for an electron is

• Millikan determined the charge and mass on the electron through his famous Oil Drop Experiment and the values                 

             were: e = -1.6 × 10^-19 C and m = 9.1 × 10^-31 kg.
 

• On calculation, it is found that e/m = E/H²r where E is strength of electric field. H is strength of magnetic field and r is the radius of the curved path taken up by the electron as it moves through the magnetic field.
• The value of e/m ratio for an electron is =1.78 × 10⁸ c/g