An electron starts from rest and is accelerated through a potential difference V. The electron moves in a path perpendicular to the magnetic field B. The path of the electron makes a circle of radius R. Which of the following gives the formula for the charge to mass ratio (e/m) of the electron?

a. e/m= 2V/B^2. R^2
b. e/m= B^2R^2/2V
c. e/m= 2VB^2/R^2
d. e/m= R^2/ 2VB^2
e. e/m = 2VR^2/ B^2
f. e/m= B^2/ 2VR^2
g. e/m= 2VB^2R^2
h. None of these