Consider a series circuit connected to an alternating–voltage source of variable…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Consider a series RLC circuit connected to an alternating–voltage source of variable angular frequency ω. The circuit elements have fixed values R, L and C.
(i) Starting from the definitions of inductive and capacitive reactance, derive an expression for the phase angle ϕ between the source voltage and the circuit current in terms of R, L, C and ω. State clearly the sign convention adopted for ϕ.
(ii) Draw a qualitative sketch of the variation of ϕ with ω, indicating the points where the current is in phase, leads, and lags the supply voltage. Mark the resonant angular frequency ω0 on the sketch.
(iii) Using your result in part (i), explain why the current leads the voltage for ω<ω0 but lags for ω>ω0. Relate your explanation to the relative magnitudes of the inductive and capacitive reactances in each region.