In an a.c. circuit, the r.m.s. value of current, i_r.m.s. is related to the peak current, i₀ by the relation:

In a circuit, L, C and R are connected in series with an altering voltage source of frequency f. The current leads the voltage by 45º. The value of C is

A coil of self-inductance L. is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when

A capacitor has capacity C and reactance X. If capacitance and frequency become double, then reactance will be:

In a series resonant circuit, having L, C and R as its elements, the resonant current is i. The power dissipated in the circuit at resonance is