\(Q^{'} = \sqrt{{\left | \underline{S} \right |}^2 - P^2}\), where \(\underline{S}\) is apparent power and \(P\) is active power.
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"Non-active Power", for a two-terminal element or a two-terminal circuit under periodic conditions, is the quantity equal to the square root of the difference of the squares of the apparent power and the active power.