A beam of cathode rays is subjected to crossed electric (E ) and magnetic fields (B). The fields are adjusted such that the beam is not deflected. The specific charge of the cathode rays is given by

Options

A. `E^2/(2VB^2)`
B. `B^2/(2VE^2)`
C. `(2VB^2)/E^2`
D. `(2VE^2)/B^2`

Answer

A

Explanation

`qvB = qE implies v = E/B`
Since, `1/2mv^2 =qV implies q/m=v^2/(2V) = E^2/(2VB^2)`