Question
Tue January 15, 2013 By:
 

Define cathode ray experiment. How is it done?

Expert Reply
Tue January 15, 2013

In 1897 ,the British physicist J.J. Thomson was able to measure the ratio of the electrical charge to the mass of the electron using a cathode ray discharge tube.

He applied electrical and magnetic field perpendicular to each other as well as to the path of the electrons.

When the magnetic field alone is turned on electron strikes the cathode ray tube at point at a point. Similarly when the electrical field alone is turned on, the electron strikes on another point above the previous point. When both the magnetic and electric fields are off or when they are balanced so as to cancel each other’s effects, the electron strikes on a point above the previous point.

By carefully and quantitatively determining the effects of magnetic and electric fields on the motion of the cathode rays, Thomson was able to determine the value of charge to mass ratio as.

Where  is mass of electron in kg ;  is magnitude of the charge on electron in coulomb.

 

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