A positively charged disc is placed on a horizontal plane. A charged particle is released from a certain height on its axis. The particle just reaches the centre of the disc. Select the correct alternative.

A current carrying ring is placed in a horizontal plane. A charged particle is dropped along the axis of the ring to fall under the influence of gravity

A current carrying ring is placed in a horizontal plane. A charged particle is dropped along the axis of the ring to fall under the influence of gravity

A thin fixed ring of radius 'R' and positive charge 'Q' is placed in a vertical plane. A particle of mass 'm' and negative charge 'q' is placed at the centre of ring. If the particle is given a small horizontal displacement, show that it executes SHM. Also find the time period of small oscillations of this particle, about the centre of ring. (Ignore gravity)

A non-conducting disc of radius a and uniform positive surface charge density sigma is placed on the ground, with its axis vertical. A particle of mass m and positive charge q is dropped, along the axis of the disc, from a height H with zero initial velocity. The particle has q//m=4 in_0 g//sigma (a) Find the value of H if the particle just reaches the disc. (b) Sketch the potential energy of the particle as a function of its height and find its equilibrium position.

If a circular concentric hole is made on a disc then about an axis passing through the centre of the disc and perpendicular to its plane

If a circular concentric hole is made on a disc then about an axis passing through the centre of the disc and perpendicular to its plane

A non-conducting disc of radius a with uniform positive surface charge density sigma is placed on the ground with its axis vertical. A particle of mass m and positive charge q is dropped along the axis of the disc from a height H with zero initial velocity. Charge per unit mass of the particle is q/m = (4 epsilon_0 g)/(sigma) . (i) Find the value of H if the particle just reaches the disc.