Question

In a region of space, a uniform magnetic field $B$ exists in the $x-$direction. An electron is fired from the origin with its initial velocity $u$ making an angle $\alpha$ with the y direction in the $yz$ plane. In the subsequent motion of the electron,

• A. $y-$coordinate of the electron will never be negative
• B. $z-$coordinate of the electron will never be negative
• C. $x-$coordinate of the electron will never be negative
• D. trajectroy of the electron would be helical

Answer 1

The correct option is C $x-$coordinate of the electron will never be negative

The trajectory of the electron will lie in the $yz$ plane since magnetic field $B$ is $\hat{i}$ direction and initial velocity $\overrightarrow{v}$ is in $yz$ plane.
$\therefore x-$coordinate of the electron will be zero always.