Given: The potential difference between collector and emitter is
The work done on the electron by the potential difference is equal to the kinetic energy of the electron.
By substituting the values in the above equation, we get
Thus, the speed of the electron is
The speed of the electron for potential difference
This value of speed is not possible because it is greater than the speed of light. The above formula is valid only for speed
When the speed of particle approaches to the speed of light, the mass of the particle starts to change according to the relation,