Pattern 1 — Drift Velocity (NEET 2018, 2020, 2023): Questions test the dependence of vd on current, area, and electron density using vd = I/(neA). Common formats: (a) "what happens to vd if diameter is doubled?" (vd halves since A quadruples with constant I); (b) "which factor does NOT affect vd?" (length of wire does not appear in vd = I/(neA)); (c) "why does current flow instantaneously even though vd is small?" (electric field propagates at ~c).
Pattern 2 — Wheatstone Bridge and Metre Bridge (NEET 2019, 2022): Direct application of P/Q = R/S. Find unknown resistance given three others. Metre bridge: apply R/S = l/(100−l), then test what happens when R and S are interchanged (l′ = 100 − l). Ensure balance point is near 50 cm for maximum sensitivity.
Pattern 3 — Potentiometer (NEET 2021, 2024): EMF comparison using ε_{1}/ε_{2} = l_{1}/l_{2} (straightforward ratio). Internal resistance: r = R(l_{1} − l_{2})/l_{2} (two readings needed). Key conceptual point: at null point, no current flows from test cell → true EMF, not terminal voltage.
Pattern 4 — Power in Series vs Parallel (Recurring): Nearly every recent NEET has a power comparison question. The formula P ∝ 1/R_eq for same battery voltage gives P_parallel/P_series = R_series/R_parallel = 3R/(R/3) = 9 for three identical resistors. Students who do not know this ratio lose this question.
Pattern 5 — Terminal Voltage and Internal Resistance (Recurring): V = ε − Ir for discharge; V = ε + Ir for charging. Given two of the three (V, ε, I or r), find the third. Often combined with power: P_internal = r; P_external = R.
Strategy: Always identify whether the circuit is series or parallel before choosing the power formula. Check potentiometer consistency (V_wire ≥ ε_test) before computing balance length.