Answer:
The direction of the electric field will be along z-direction.
Explanation:
When electrons enter in a region where there is only magnetic field, then force exerted by the magnetic field will be
[tex]\vec{F_{B}} = e(\vec{v} \times \vec{B})[/tex]
This force will deflect the electron in a direction perpendicular to its motion and also perpendicular to the magnetic field.
Whereas in the presence of electric field, force exerted by the electric field is
[tex]\vec{F_{E}} = e\vec{E}[/tex]
The direction is opposite to the direction of electric field.
As a result, electron deflected by magnetic field is nullified by the deflection by electric field. As a result, electron moves undeflected.
So, if the direction of the magnetic field is along y-direction, the direction of the electric field has to along z-direction.
