Points to Ponder

When an AC voltage or current value is given without qualification, it is always the rms value. For example, the 240 V from a household outlet is the rms voltage. The peak amplitude is $V_m = \sqrt{2} \times 240 \approx 340\ \text{V}$.

The power rating marked on any AC device (like a bulb or heater) indicates its average power consumption over a full cycle, not the instantaneous peak power.

In an AC circuit, the instantaneous power can be positive or negative, but the average power is never negative — it is always zero or positive, because energy is only dissipated (not generated) by the circuit elements.

The ampere for AC cannot be defined by the magnetic force between two parallel wires (as for DC), because the force would average to zero due to the changing current direction. Instead, the rms ampere is defined by Joule heating: 1 A rms AC produces the same average heating effect in a resistor as 1 A DC.

When adding voltages across different components in an AC circuit, you must account for phase differences. For example, in an RC circuit, the voltage across the resistor ($V_R$) and capacitor ($V_C$) are $90^\circ$ out of phase, so the total voltage is $V_{RC} = \sqrt{V_R^2 + V_C^2}$, not $V_R + V_C$.

Although phasor diagrams use arrows like vectors, voltage and current are scalar quantities — they only have magnitude and phase, not direction in space. Phasors are a mathematical tool that mimics vector addition to simplify the combination of sinusoidal quantities.

In an AC circuit, pure inductors and capacitors do not dissipate energy — they store and release it. Only resistors convert electrical energy into heat, so power loss occurs only in resistive elements.

Resonance in an RLC circuit occurs when the inductive reactance equals the capacitive reactance: $X_L = X_C$, or $\omega = \frac{1}{\sqrt{LC}}$. Resonance is impossible if either $L$ or $C$ is missing, because there is no cancellation of reactive voltages.

The power factor (cos $\phi$) in an RLC circuit indicates how close the circuit is to delivering maximum average power. A power factor of 1 means all power is real (resistive), while 0 means no real power is consumed. …