An RC circuit consists of a capacitor and resistor connected in series to an AC source as shown above (the green circle labeled V+ is just a voltmeter that is used to measure the voltage drop across the capacitor).  The frequency of the voltage source can be adjusted with the slider.  The voltage drops across the resistor and capacitor do not seem to add up to the source voltage.  That is, V_r + V_c = V_s does not seem to be true in this circuit.  Does this violate Kirchhoff's loop rule for voltage?   Start.