RLC series a.c. circuit
Related Applets:
Resonance in Mechanics:Force Object to Oscillate through the Action of Spring
Resonance in Waves: Generate Stationary Waves in a String
Resonance in Electricity: RLC Parallel Resonance
The small square at the left of each waveform shows the instantaneous value.  




The subscripts "o" and "rms" stand for peak value and rootmeansquare value respectively.  
The supply voltage (A) and the circuit current (E) will always have a phase difference. The phase difference can be found by using the triangle (H). If the inductive reactance is greater than the capacitive reactance, the supply voltage will lead the current; if the inductive reactance is smaller than the capacitive reactance, the supply voltage will lag behind the current .  
The p.d. across the resistor (B) oscillates inphase with the current (E).  
The p.d. across the capacitor (C) lags behind the current (E) by pi/2.  
The p.d. across the inductor (D) leads the current (E) by pi/2.  
.In other words, (C) and (D) are wlays in antiphase.  
The four RMS volatges are related by the triangle (H).  
The curve (F) shows the variation of the reciprocal of the impedance against frequency.  
(G) shows three rotating vectors (phasors), their projections on the yaxis corresponds to the three instantaneous voltages. 

Series resonance is achieved by adjusting f, L or C such that the black dot is exactly at the highest point of the curve (F).  
At resonance, (i) phase diff = 0 and (ii) Z = R. Therefore, (A) and (B) become exactly identical, (A) and (E) are inphase. The circuit current (E) is the greatest.  
At resonance, the p.d. across the capacitor (C) and that across the inductor (D) may be large in magnitude but their sum is zero.  