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Cheat sheet · NEET Preparation Physics

Alternating Current cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

NEET · Physics

Cheat sheet

Class 12 · Chapter 7Alternating Current

ELI the ICE man: in L, voltage leads current; in C, current leads voltage.

1. RMS Values

Irms=I02I_{rms} = \dfrac{I_0}{\sqrt2}Vrms=V02V_{rms} = \dfrac{V_0}{\sqrt2}

2. Circuits

CircuitReactancePhase
RRin phase
LXL=ωLX_L = \omega LV leads I by 90°
CXC=1ωCX_C = \dfrac1{\omega C}I leads V by 90°
Z=R2+(XL−XC)2Z = \sqrt{R^2 + (X_L - X_C)^2}tan⁡ϕ=XL−XCR\tan\phi = \dfrac{X_L - X_C}{R}

3. Resonance & Power

ω0=1LC\omega_0 = \dfrac{1}{\sqrt{LC}}Q=ω0LRQ = \dfrac{\omega_0L}{R}
P=VrmsIrmscos⁡ϕP = V_{rms}I_{rms}\cos\phi

Power factor cos φ; wattless current when φ = 90°.

4. Transformer

VsVp=NsNp=IpIs\dfrac{V_s}{V_p} = \dfrac{N_s}{N_p} = \dfrac{I_p}{I_s}

Losses: copper, eddy current, hysteresis, flux leakage.

5. Key Points

  • At resonance Z = R, current maximum.
  • Step-up: Ns > Np.
  • AC can't be used for electrolysis directly.
  • LC oscillations: energy swaps between L and C.

Remember: rms | X_L, X_C, Z | resonance | transformer ratio

Alternating Current: questions and notes

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