A thin ring with resistance R=10 Ω and self inductance L=0.2 H rotates with constant angular speed ω=100 rad/s in an external uniform magnetic field perpendicular to the rotation axis. As a result, the magnetic flux created by the external field varies with time as

Question

A thin ring with resistance R=10 Ω and self inductance L=0.2 H rotates with constant angular speed ω=100 rad/s in an external uniform magnetic field perpendicular to the rotation axis. As a result, the magnetic flux created by the external field varies with time as
Φ(t)=Φ0cos(ωt)whereΦ0=0.1 Wb.
Because of the resistance of the ring, energy is being continuously dissipated in the system. What average power Pˉ in Watts must develop the external forces to keep the ring rotating at constant angular speed ω (on average).