The Betatron was the first important machine for producing high energy electrons. The action of the betatron depends on the same fundamental principle as that of the transformer in which an alternating current applied to a primary coil induces an altermating current usually with higher or lower voltage in the secondary coil. In the betatron secondary coil is replaced by a doughnut shaped vacuum chamber.Electron produced in the doughnut from a hot filament, are given a preliminary acceleration by the application of an electric field having potential difference of `20 kV` to `70 kV`, when an alternating magnetic field is applied parallel to the axis of the tube, two effects are produced `(1)` an electromotive force is produced in the electron orbit by the changing magnetic flux that gives an additional energy to the electrons `(2)` a radial force is produced by the action of magnetic field whose direction is perpendicular to the electron velocity. Which keeps the electron moving in a circular path. Conditions are arranged such that the increasing magnetic field keeps the electron in a circular orbit of constant radius. The mathematical relation between the betatron parameters to ensure the above condition is called `BETATRON` condition. If the orbit radius of the circular path traced by the electron is `R`, magnetic field is `B`, speed of the electron is `v`, mass of the electron is `m`, charge on the electron is `e` and `phi` is the flux within the orbit of radius `R`. Then answer the following questions based on the above comprehension. What is the value of `(d(m|vecv|))/(dt)` ?