# There is a non conducting ring of radius R charge q. Uniform magnetic field exist in circular region concentric with ring of radius r < R, which varies as dB/dt=k. Torque on ring is? [ Ans (k.q.r^2)/2 ] PLEASE POST SOLUTION

Arun Kumar IIT Delhi
8 years ago
$\int E.ds=-d\phi/dt \\=>E.2\pi R=-\pi r^2k \\=>E=-\pi r^2k/2\pi R=r^2k/2R \\=>T=Q*R*E=Q*R*r^2/2R$

Thanks & Regards
Arun Kumar
IIT Delhi