If an electron enters a magnetic field with its velocity pointing in the same direction as the magnetic field, then

Explain electric field and its source as well as magnetic field and its source.

The radius of circular path of an electron when subjected to a perpendicular magnetic field is

A current carrying long solenoid is placed on the ground with its axis vertical. A proton is falling along the axis of the solenoid with a velocity $v$. When the proton enters into the solenoid, it will

A particle of charge $q$ and mass $m$ is moving with a velocity $-v \hat{ i }(v \neq 0)$ towards a large screen placed in the $Y – Z$ plane at a distance $d.$ If there is a magnetic field $\overrightarrow{ B }= B _{0} \hat{ k },$ the minimum value of $v$ for which the particle will not hit the screen is