For the LCR circuit, the energy dissipated over a long time is \(U = (V_{rms}I_{rms}cos\phi)t\). When resistance is removed, the circuit becomes LC circuit, the impedance and hence current changes.
The circuit is as shown in figure. One time cycle \(T = \frac{2\pi}\omega = \frac{2\pi}{314} = 0.02s\). So, we have to calculate the average energy at time t>>T.
Energy dissipated in time t
When resistance is removed, and inductance is doubled, then cosφ = 0 ⇒ φ = π/2
Value of impedance is
And the current in the circuit is found to be
