A magnetic field
\(\vec B = \left(\vec a_x + 2\vec a_y-4\vec a_z\right)\)
exists at a point. If a test charge moving with a velocity
\(\vec V = V_0 \left(3 \vec a_x - \vec a_y + 2 \vec a_z\right)\)
experiences no force at a certain point, the electric field at that point will be
1
\(\vec E = -V_0 \left( 3 \vec a_x - 2 \vec a_y - 4 \vec a_z\right)\)
2
\(\vec E = -V_0 \left(14 \vec a_y + 7 \vec a_z\right)\)
3
\(\vec E = -\frac {V_0}{\mu}\left(14 \vec a_y + 7 \vec a_z\right)\)
4
\(\vec E = +\frac {V_0}{\mu}\left(14 \vec a_y + 7 \vec a_z\right)\)