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Beyond the textbook: circuits with several branches, phasor diagrams drawn from measurements, resonance of parallel circuits, and energy exchange between a coil and a capacitor. The problems that JEE, NEET and A-Level Physics ask most, with a full timed paper.

What's inside

1. Branched AC circuits: When parts of a circuit are in parallel, every branch has the same voltage, and the currents add as arrows, not as numbers. The component method splits each branch current into a part in phase with the voltage and a part a quarter of a turn away. Admittance and complex numbers do the same sums quickly.
2. Phasors from measurements: A meter shows a size and hides the phase. But the sizes of three voltages in a series loop fix a triangle, and the triangle gives the angle. The same works for three ammeters in a parallel circuit. An oscilloscope shows a phase as a delay, or as an ellipse whose crossing height gives the sine of the phase.
3. Energy in LC and parallel circuits: At resonance a series circuit keeps a fixed amount of energy that moves between the coil and the capacitor, and the source only pays for the heat in the resistance. That gives $Q = 2\pi \times$ (energy stored) / (energy lost per cycle). A coil and a capacitor in parallel resonate too, but the line current is smallest. With a real coil the impedance peaks at $R_d = L/(Cr)$