Question

A collimated beam of protons is travelling with a constant velocity along X-axis There is a current carrying solenoid whose axis is also X-axis. If the beam now enters the solenoid along its axis, it will ______

Options

• describe a circular path.

• get deflected along Z-axis.

• get deflected along Y-axis.

• continue to travel undeflected.

Answer 1

A collimated beam of protons is travelling with a constant velocity along X-axis There is a current carrying solenoid whose axis is also X-axis. If the beam now enters the solenoid along its axis, it will continue to travel undeflected.

Explanation:

 Inside a (long) solenoid the magnetic field points along the solenoid’s axis, i.e., along the X‑axis in your setup. The magnetic force on a charge is F = q v × B; when the proton velocity v is parallel to B the cross product is zero, so there is no magnetic force to deflect the beam.

Hence a beam entering along the solenoid axis continues undeflected.