CURRENT ELECTRICITY — NEET 2026 CHEAT SHEET

Core Formulas:

Combinations:

• Series: R_eq = $R_{1}$ + $R_{2}$ (same I; V divides)
• Parallel: 1/R_eq = 1/$R_{1}$ + 1/$R_{2}$ (same V; I divides)
• Power (same battery): P_parallel = $n^{2}$ × P_series

Temperature:

• Metals: α > 0 (R increases with T)
• Semiconductors: α < 0 (R decreases with T)
• Alloys (manganin): α ≈ 0

Kirchhoff's Laws:

• KCL: ΣI = 0 (charge conservation)
• KVL: Σ$\Delta V$ = 0 (energy conservation)
• Sign: −IR (with current); +IR (against); +ε (− to +); −ε (+ to −)

Null Methods:

• Wheatstone bridge: P/Q = R/S → Ig = 0
• Metre bridge: R/S = l/(100−l); interchange → l′ = 100−l
• Potentiometer: ε_{1}/ε_{2} = l_{1}/l_{2}; r = R(l_{1}−l_{2})/l_{2}; TRUE EMF (no current at null)

NEET Traps:

1. Potentiometer → TRUE EMF (not terminal voltage)
2. Series power: P = $I^{2}$R (same I) | Parallel power: P = $V^{2}$/R (same V)
3. P_parallel = $n^{2}$ × P_series (for same battery)
4. Metre bridge interchange: l′ = 100 − l
5. Short circuit: V_terminal = 0; I = ε/r
6. Semiconductor: R DECREASES with temperature