Q.

A current carrying solenoid is placed vertically and a particle of mass m with charge Q is released from rest. The particle moves along the axis of solenoid. If g is acceleration due to gravity then the acceleration (a) of the charged particle will satisfy :   [2026]

1 a > g  
2 a = g  
3 0 < a < g  
4 a = 0  

Ans.

(2)

Since the solenoid is placed vertically, the magnetic field inside the solenoid will be either along -y or +y axis.

⇒  Particle will gain velocity along -y axis.

⇒  F→B=q(v→×B→)

⇒  F→B=0

⇒  F→net=mg→

⇒  anet=g