PhysicsElectric Current

Effective Study Strategies

• Master Ohm’s Law: V = IR. Understand both directions: I = V/R and R = V/I. Practice with different units.
• Differentiate EMF and terminal voltage: EMF (E) = work per unit charge by battery. Terminal voltage V_t = E – Ir (discharging) or V_t = E + Ir (charging).
• Understand series and parallel combinations: Series: R_eq = R₁ + R₂ + …, same current. Parallel: 1/R_eq = 1/R₁ + 1/R₂ + …, same voltage.
• Practice Kirchhoff’s rules: Junction rule: ΣI_in = ΣI_out. Loop rule: ΣV = 0. Choose consistent sign conventions.
• Calculate electrical power: P = VI = I²R = V²/R. Understand which formula to use based on given quantities.
• Work with resistivity: R = ρL/A. ρ depends on material and temperature. α = (R_t – R₀)/(R₀t) for temperature coefficient.
• Apply Wheatstone bridge principle: Balanced when R₁/R₂ = R₃/R₄. No current through galvanometer when balanced.
• Understand potentiometer applications: V ∝ L for uniform wire. Can compare EMFs without drawing current from cells.

Exam Preparation Tips

• Memorize key formulas on flashcards: I = q/t, V = IR, R = ρL/A, P = VI, V_t = E ± Ir, α = ΔR/(R₀Δt).
• Practice circuit analysis: Simplify complex circuits using series/parallel combinations. Use Kirchhoff’s rules for complex networks.
• Solve Wheatstone bridge problems: Identify balanced/unbalanced conditions. Calculate unknown resistances.
• Understand color codes: Remember resistor color bands: Black(0), Brown(1), Red(2), Orange(3), Yellow(4), Green(5), Blue(6), Violet(7), Gray(8), White(9).
• Practice unit conversions: 1 A = 1 C/s, 1 Ω = 1 V/A, 1 W = 1 J/s = 1 V·A, 1 kWh = 3.6×10⁶ J.
• Time yourself on complex circuits: Set timer for 4-6 minutes per complex circuit problem.

Common Pitfalls to Avoid

• Confusing conventional current (positive to negative) with electron flow (negative to positive)
• Mixing up series and parallel resistor formulas
• Forgetting internal resistance in battery problems: V_t ≠ E when current flows
• Using wrong power formula: P = I²R for constant R, P = V²/R for constant V, P = VI always works
• Not considering temperature effects on resistance: R increases with T for metals, decreases for semiconductors
• Forgetting that resistivity (ρ) is material property, resistance (R) depends on dimensions
• Misinterpreting resistor color codes or tolerance bands
• Applying Ohm’s Law to non-ohmic materials (diodes, filament lamps)