Question

The monoenergetic beams of electronics moving along + y direction enters a region of uniform electric and magnetic fields. If the beam goes straight through, then in which direction these simultaneously field $\overrightarrow{B}$ and $\overrightarrow{E}$ are directed ?

Answer 1

Force of monoenergetic beam of electrons due to magnetic field $=\overrightarrow{V}\times \overrightarrow{B}$

B = magnetic field

V = velocity of electrons

and force is perpendicular to magnetic field direction

Force due to electric field$=q\overrightarrow{ϵ}$

$q=$magnitude of charge

$\overrightarrow{ϵ}$ = electric field

direction of force due to electric field is parallel to velocity of beam.

If beam of electrons pass straight it means no force due to magnetic field that implies magnetic field and velocity are parallel and electric field also parallel to electrons.

Direction of magnetic field = y axis

Direction of electric field = y axis

Only then it is possible when beam of electrons went straight.