(i) The impedance of a series LCR circuit is given by will be minimum when ωL=1/ωC, i.e., when the circuit is under resonance. Hence, for this condition, Z will be minimum and will be equal to R.

(ii) Average power dissipated through a series LCR circuit is given by Pav=EvIvcosϕ where, Ev = rms value of alternating voltage Iv = rms value of alternating current Φ = phase difference between current and voltage For wattless current, the power dissipated through the circuit should be zero. i.e., cosϕ=0⇒ϕ=π2 Hence, the condition for wattless current is that the phase difference between the current and voltage should be π/2 and the circuit is purely inductive or purely capacitive.

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