Question

A uniform electric field E = 80kV/m is directed down on this page. A magnetic field B = .4 T is directed into this page. Find the speed at which a charge will not be deflected by this arrangement of field (called a velocity selector). Why does this selection not depend on the charge q of the particle?

Answer 1

Force due to electric field is
\[F _{1}=qE\]
Force due to magnetic field is
\[F _{2}= q(v \times B)\]
Equate it
\[E=v \times B\]
\[v=E \div B\]
\[v=2\times 10^{5} m/s\]