Physics · Class 12 · Chapter 7
Alternating Current
10 lessons 73 min 2 simulations
The mains supply alternates, so this chapter works out how resistors, inductors and capacitors behave when the voltage across them follows a sine curve. It introduces rms values so that ac power looks like dc power, uses rotating phasors to track phase, defines reactance and impedance, finds the resonance of a series LCR circuit, shows why only the in-phase part of the current uses power, and ends with the transformer that makes ac the choice for power supply.
What the exam asks
NEET sets direct numericals on rms and peak values, XL = ωL and XC = 1/ωC, impedance Z = √(R² + (XL − XC)²), the phase angle, resonant frequency 1/2π√(LC), average power VI cos φ and transformer ratios. Conceptual items ask which element leads or lags, what happens to current when frequency changes, and when the power is zero. Marks are lost by adding VR and VC directly, by mixing peak and rms values, and by forgetting that an ideal transformer keeps power, not current, the same.
Lessons
10 lessons · 73 min
1Alternating voltage and a resistorNCERT §7.1, §7.25 min2RMS values and average powerNCERT §7.26 min3PhasorsNCERT §7.35 min4AC through an inductorNCERT §7.45 min5AC through a capacitorNCERT §7.510 min 1 sim6Series LCR circuit and impedanceNCERT §7.6, §7.6.16 min7ResonanceNCERT §7.6.29 min 1 sim8Power factorNCERT §7.76 min9TransformersNCERT §7.86 min10Chapter reviewMust-know facts, traps and formulas15 min