The figure shows a resistor, an inductor and a capacitor in series with an alternating source of constant rms voltage. Three voltmeters read the rms voltages across them: $60\ \text{V}$, $100\ \text{V}$ and $20\ \text{V}$. The frequency of the source is then changed until the arrangement is in resonance. The source voltage and the resistance stay the same. What does the voltmeter across the resistor read now?

Fig. 1: A series circuit in a single loop with an alternating voltage source at the left, a resistor R, an inductor L and a capacitor C. Three voltmeters, drawn as circles with a V, are joined across R, across L and across C. The readings written beside them are 60 V across R, 100 V across L and 20 V across C. The source is labelled with a question mark in place of its voltage.