Ch 7 covers AC circuits — RMS values, phasor diagrams, R/L/C circuits, LCR series circuit, resonance, quality factor, power, and transformers.
AC: v = V₀ sin ωt. RMS values: V_rms = V₀/√2, I_rms = I₀/√2. Reactance: X_L = ωL (inductor, V leads I by 90°), X_C = 1/ωC (capacitor, V lags I by 90°). Impedance of LCR series: Z = √(R² + (X_L−X_C)²). Phase angle: tan φ = (X_L−X_C)/R.
Resonance: X_L = X_C → Z = R (minimum impedance, maximum current). Resonant frequency f₀ = 1/(2π√LC). Quality factor Q = ω₀L/R. Power: P = V_rms I_rms cos φ (cos φ = power factor). At resonance, cos φ = 1 (maximum power). Transformer: V₂/V₁ = N₂/N₁ = I₁/I₂. Step-up: N₂ > N₁. Step-down: N₂ < N₁. Energy losses: copper, eddy currents, hysteresis, flux leakage.
Download: https://ncert.nic.in/textbook/pdf/leph107.pdf | Part I: https://ncert.nic.in/textbook/pdf/leph1ps.zip
AC can be easily stepped up to high voltage using a transformer. At high voltage, the current is lower (P = VI), which reduces I²R losses in transmission lines. At the receiving end, transformers step the voltage back down. DC cannot be easily transformed to different voltages, so AC is preferred for transmission.
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