An electron is projected with velocity $v_0$ in a uniform electric field $E$ perpendicular to the field. Again,it is projected with velocity $v_0$ perpendicular to a uniform magnetic field $B$. If $r_1$ is the initial radius of curvature just after entering the electric field and $r_2$ is the initial radius of curvature just after entering the magnetic field,then the ratio $r_1:r_2$ is equal to:

• A
  $\frac{Bv_0^2}{E}$
• B
  $\frac{B}{E}$
• C
  $\frac{Ev_0}{B}$
• D
  $\frac{Bv_0}{E}$