AC Source & Phasor
v(t) = V₀ sin(ωt). Rotating phasor projects onto sine wave. V_rms = V₀/√2.
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Class 12 · Notes
Alternating Current— Notes, Formulas & Revision
Complete revision notes and formulas for Alternating Current (Class 12). Curated for JEE, NEET, AP Physics, SAT, and CUET. Tap any topic to open the live simulation and full PYQ set.
AC through Resistor
I in phase with V (φ = 0°). I₀ = V₀/R.
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AC through Inductor
I lags V by 90°. X_L = ωL grows with frequency.
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AC through Capacitor
I leads V by 90°. X_C = 1/(ωC) falls with frequency.
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Series LCR Circuit
Z = √(R² + (X_L − X_C)²). Phasor + impedance triangle live.
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LCR Resonance
I peaks at f₀ = 1/(2π√LC). Q-factor and bandwidth Δf = f₀/Q.
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Power & Power Factor
P_avg = V_rms·I_rms·cosφ. Watch p(t) = v·i and the average line.
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LC Oscillations
q(t) = q₀cos(ω₀t). Energy bounces between capacitor and inductor.
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Transformer
V_s/V_p = N_s/N_p. Step-up vs step-down with animated flux in core.
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AC Generator
ε(t) = NBAω sin(ωt). Rotating coil between magnetic poles.
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Reactance vs Frequency
X_L (linear ↑) and X_C (1/f ↓) crossing at resonance frequency f₀.
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RMS Values
V_rms = V₀/√2 — DC equivalent for power. Mains 230 V is RMS, peak 325 V.
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Phasor Addition (V_R, V_L, V_C)
Vector sum: V = √(V_R² + (V_L − V_C)²). Tune each and see V_net.
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Alternating Current on sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs). Free physics revision for Class 12, JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT Subject Physics, and CUET-UG.