A proton is moving towards the north along a horizontal line passes through a zero-gravity region, where the electric and magnetic field is mutually perpendicular to each other. The path of particles remains underived or undeflected. If the direction of the electric field is toward the east then the direction of the magnetic field is:

A proton goes undeflected in a crossed electric and magnetic field (the fields are perpendicular to each other) at a speed of $2.0\times 10^{5}m{s}^{-1}$.The velocity is perpendicular to both the fields. When the electric field is switched off, the proton moves along a circle of radius $4.0cm$. Find the magnitudes of the electric and the magnetic fields. Take the mass of the proton = $1.6\times 10^{-27}kg$.