Magnetic field physics question?

Question

A velocity selector in a mass spectrometer, uses a 0.100 T magnetic field. What electric field strength is needed to select a speed of 4.00*10^6 m/s? What is the voltage between the plates if they are seperated by 1.00 cm?

Answer 1

I think I got the units right, it's been a long time.

Fe = qE

Fb = qvB

qE = qvB

E = vB

E = 4.0e6 m/s * 0.100 V s/m²

E = 4.0e5 V/m

V = 4.0e5 V/m * 0.01m

V = 4.0e3 V

Answer 2

E = vB, and V = E/d.