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Current Electricity
Ohm's law, Kirchhoff's laws, Wheatstone bridge
Key Concepts
- Ohm's law: V = IR (valid for ohmic conductors at constant temperature)
- Resistivity depends on material and temperature; ρ = ρ₀(1 + αΔT)
- Kirchhoff's current law (KCL): sum of currents at junction = 0
- Kirchhoff's voltage law (KVL): sum of EMFs = sum of IR drops in a loop
- Wheatstone bridge: balanced when R₁/R₂ = R₃/R₄
Important Formulae
| Ohm's law | V = IR |
| Resistance | R = ρL/A |
| Power | P = VI = I²R = V²/R |
| EMF with internal resistance | V = E − Ir |
| Resistors in series | R_s = R₁ + R₂ + ... |
| Resistors in parallel | 1/R_p = 1/R₁ + 1/R₂ + ... |
Quick Tips
- Maximum power transferred to external resistance when R_ext = r (internal resistance).
- Drift velocity: v_d = I/(nAe); typically very small (~mm/s) but electrons signal at ~c.
- Colour code for resistors: BBROYGBVGW (0–9): Black Brown Red Orange Yellow Green Blue Violet Grey White.
Practice Questions
Practice 20 randomly selected NEET questions on Current Electricity. Answers are revealed after each question.
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