Question

The beam of electrons goes undeflected when passing through crossed electric and magnetic fields of magnitude 1.37x104 V/m and 2.89x10-3 T, respectively. What is the radius of the electron orbit, in mm, if the electric field is turned off?

Answer 1

The correct answer for this question is this one: "92.95"

We know that
Math Processing Error]

V = square root (PR)

P here would be the 1.2 Watts
R would be the 7200 ohm (notice the conversion from 7.2k ohm)

V = square root [ (1.2)(7200) ]
V = 92.95

Hope this helps answer your question and have a nice day ahead.