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Alternating Current formula sheet

Every formula in the Alternating Current chapter for JEE Main, with one line on when it applies. Topic 1 is open to everyone; sign in free to read all 19 and download the PDF.

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How we count: 7× asked means 7 past JEE Main questions in the PrepWiser bank needed that formula, and "last" is the latest year one appeared. ★ marks formulas asked 8 or more times.

AC voltage and current

Sinusoidal AC
8× asked, last 2025
i=I0sin⁡(ωt+ϕ),ω=2πf=2πTi=I_0\sin(\omega t+\phi),\qquad \omega=2\pi f=\frac{2\pi}T
Mains 50 Hz, T=20T=20 ms. Zero to peak T/4T/4, peak to rms T/8T/8, half-peak to peak T/6T/6.
Peak, rms and average
11× asked, last 2025
Irms=I02,Iˉhalf cycle=2I0π,Iˉfull cycle=0I_{\text{rms}}=\frac{I_0}{\sqrt2},\qquad \bar I_{\text{half cycle}}=\frac{2I_0}\pi,\qquad \bar I_{\text{full cycle}}=0
Sine only. Meters and 220 V mains are rms. Heating uses rms (half of DC I0I_0).
rms of any waveform
7× asked, last 2026
Irms=1T∫0Ti2 dt,Irms=Idc2+I022I_{\text{rms}}=\sqrt{\frac1T\int_0^Ti^2\,dt},\qquad I_{\text{rms}}=\sqrt{I_{\text{dc}}^2+\frac{I_0^2}2}
Square I0I_0, triangle I0/3I_0/\sqrt3, half-wave I0/2I_0/2. I1sin⁡ωt+I2cos⁡ωtI_1\sin\omega t+I_2\cos\omega t: (I12+I22)/2\sqrt{(I_1^2+I_2^2)/2}.

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16 more formulas in 5 topics

AC circuits: R, L, C; Series RLC circuit; Resonance, Q-factor and LC oscillations; Power in AC circuits; and Transformers. Read the first part free. Sign in free with Google to read the rest and download the PDF.

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AC circuits: R, L, C

  • Phase in pure R, L, C8×
  • Inductive reactance10×
  • Capacitive reactance6×

Series RLC circuit

  • Impedance19×
  • Phase angle12×
  • Voltages add as phasors4×
  • RL and RC circuits14×

Resonance, Q-factor and LC oscillations

  • Series resonance33×
  • Quality factor8×
  • LC oscillations5×

Power in AC circuits

  • Average power15×
  • Power factor12×
  • Choke coil with a lamp4×

Transformers

  • Ideal transformer6×
  • Efficiency2×
  • Transmission loss

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About 135 past JEE Main questions from this chapter, with instant answer checking and step-by-step solutions where available. Free, and you can start without signing up.

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Version 1, October 2026. Free to share for study, as it is. Please don't sell it or remove the PrepWiser name.

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