RMS (root mean square) value: I_rms = I₀/√2, V_rms = V₀/√2 (for sinusoidal AC).

Peak value I₀ = √2 I_rms.

Average value over half cycle: I_avg = (2I₀)/π.

Resonance: when X_L = X_C → ωL = 1/(ωC) → ω₀ = 1/√(LC), f₀ = 1/(2π√(LC))

At resonance: Z_min = R, I_max = V/R, current and voltage in phase.

Step‑up transformer: N_s > N_p → V_s > V_p, I_s < I_p.

Step‑down transformer: N_s < N_p → V_s < V_p, I_s > I_p.

💡 NEET TIPS & SHORTCUTS

• At resonance, impedance is minimum, current is maximum, and power factor = 1.
• For LCR circuit, the peak current occurs at resonance frequency.
• Power factor cos φ = R/Z. For pure L or C, cos φ = 0.
• In AC circuits, average power is dissipated only in resistor.

⚠️ COMMON MISTAKES

• Using DC formulas for AC (e.g., V = IR for L or C).
• Forgetting that reactances depend on frequency (X_L ∝ f, X_C ∝ 1/f).
• Confusing phase relationships (voltage leads current in inductor, lags in capacitor).
• Using peak values instead of RMS in power formulas.

RMS: I_rms = I₀/√2, V_rms = V₀/√2

Impedance: Z = √[R² + (X_L – X_C)²]

Resonance: ω₀ = 1/√(LC), f₀ = 1/(2π√(LC))

Power factor: cos φ = R/Z

Avg power: P = V_rms I_rms cos φ

Transformer: V_s/V_p = N_s/N_p = I_p/I_s