In a certain region static electric and magnetic fields exist. The magnetic field is given by $\vec B = {B_0}\left( {\hat i + 2\hat j - 4\hat k} \right)$. If a test charge moving with a velocity $\vec v = {v_0}\left( {3\hat i - \hat j + 2\hat k} \right)$ experiences no force in that region, then the electric field in the region, in $SI\, units$, is
$\vec E = - {v_0}{B_0}\left( {3\hat i - 2\hat j - 4\hat k} \right)$
$\vec E = - {v_0}{B_0}\left( {\hat i + \hat j + 7\hat k} \right)$
$\vec E = {v_0}{B_0}\left( {14\hat j + 7\hat k} \right)$
$\vec E = - {v_0}{B_0}\left( {14\hat j + 7\hat k} \right)$
A beam of ions with velocity $2 \times {10^5}\,m/s$ enters normally into a uniform magnetic field of $4 \times {10^{ - 2}}\,tesla$. If the specific charge of the ion is $5 \times {10^7}\,C/kg$, then the radius of the circular path described will be.......$m$
An electron enters a region where magnetic $(B)$ and electric $(E)$ fields are mutually perpendicular to one another, then
Two ions having same mass have charges in the ratio $1: 2$. They are projected normally in a uniform magnetic field with their speeds in the ratio $2: 3$. The ratio of the radii of their circular trajectories is -
An electron moving with a speed $u$ along the positive $x-$axis at $y = 0$ enters a region of uniform magnetic field $\overrightarrow B = - {B_0}\hat k$ which exists to the right of $y$-axis. The electron exits from the region after some time with the speed $v$ at co-ordinate $y$, then
A charge $+ Q$ is moving upwards vertically. It enters a magnetic field directed to the north. The force on the charge will be towards