Practice question

**AC through capacitor** voltage lags current by 90°, Q= C V, I= dQ/dt = C dV/dt, V(t)=V_peak sin ωt, I(t)=I_peak sin(ωt+90°), average power zero because energy stored in electric field ½ C V² returned each cycle, capacitor blocks DC but passes AC, X_C decreases with f. In an RC series circuit, the circuit is predominantly capacitive if the capacitive reactance ( X_C = (1/ω C) ) is greater than the resistance ( R ). This makes the impedance Z = √(R² + X_C²) dominated by X_C , and the current leads the voltage significantly. Applying X_L = ωL, X_C = 1/ωC, Z = √(R² +