Question

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

Answer 1

Correct Answer - D
`qvB=qEimplies V=(E )/(B)`
But`(1)/(2)mv^(2)=qV so (q)/(m)=(v^(2))/(2V)=(E ^(2))/(2VB^(2))`