Question

A positive charge Q is uniformly distributed along a circular ring of radius R. A small test charge q is placed at the center of the ring figure. Then which statement is incorrect:

• A. If q>0 and is displaced away from the centre in the plane of the ring,it will be pushed back towards the centr
• B. if q<0 and is displaced away from the centre in the plane of the ring,it will never return towards the centre and will continue moving till it hits the ring
• C. ifif q>0, it will perform SHM for small displacement along the axis
• D. q at the centre of the ring is in an unstable equilibrium within the plane of the ring q>0

Answer 1

Answer: (C)

ifif q>0, it will perform SHM for small displacement along the axis

$(+ve)$ charge$=Q$

Radius$=R$

A small test charge$=q$

It is a SHM because if and only if $q>0$ it will perform like this,

$T=\frac{1}{2\pi }\sqrt{\frac{q}{r}}=\frac{1}{2\pi }\sqrt{\frac{R}{C}}$