Talk:E/m raito

e/m ratio stands for charge-to-mass ratio of the electron.

The modern value for the charge on the electron (to four significant places) is 1.602 x 10-19 coulombs and the electrons mass is 9.109 x 10-31 kilograms.

Therefore, the modern value for the e/m ratio is 1.759 x 1011 C/kg. Usually, grams are used rather than kilograms giving a numerical value of 1.759 x 108. Often, books round off the 1.759 portion to 1.76.

However, there is one problem. Many textbooks and articles use the m/e ratio, that is the mass-to-charge ratio. Reversing the above figures and using grams rather than kilograms gives a value of 5.686 x 10-9 g/C.

The e/m ratio is important because that is as far as Thomson could get with his cathode ray tubes. Knowledge of the value of 'e' or of 'm' would be needed to get to the other once you knew e/m, which Thomson did know.

Elsewhere you will find discussion of how the value for 'e,' the charge on the electron was determined. (May 1996: This will be made a link when that section is written.)