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

With the simplified model of the eye, what corrective lens (specified by focal length as measured in air) would be needed to enable a person underwater to focus an infinitely distant object? (be careful-the focal length of a lens underwater is not the same as in air! assume that the corrective lens has a refractive index of 1.62 and that the lens is used in eyeglasses, not goggles, so there is water on both sides of the lens. assume that the eyeglasses are 1.90