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.
Sample Practice Questions
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Resistivity of a material depends on:
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Answer: Nature of material and temperature
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SI unit of resistivity:
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Answer: Ω·m
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For maximum power transfer from cell to external resistance, external resistance must equal:
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Answer: Internal resistance
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Temperature coefficient of resistance for metals is:
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Answer: Positive
Practice Questions
Practice 20 randomly selected NEET questions on Current Electricity. Answers are revealed after each question.
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What are the key concepts in Current Electricity for NEET?
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.
Which formulae are important for Current Electricity in NEET?
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 + ....
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