Question

The current in a series RLC circuit lags the EMF by $20°$. You cannot change the EMF. What two different things could you do to the circuit that would increase the power delivered to the circuit by the EMF?

Short answer

Increasing capacitive reactance or decreasing inductive reactance.

Step-by-step solution

Step 1. Given information

We have been given that current lags EMF by $20°$. EMF cannot be changed.

Step 2. Solving

Current lags behind EMF so $V_l>V_c$and in order to deliver maximum power we need to get the angle between current and EMF phasor to be $0°$as resultant power contains a factor of $\cos \left(\right)$of that angle.

In order to do so we can either increase $V_c$by increasing capacitive reactance or decrease $V_l$by decreasing inductive reactance such that finally $V_l=V_c$.