🔍 Introduction
Current electricity refers to the flow of electric charge (generally electrons) through a conductor. This chapter covers electric current, Ohm’s law, resistance, combination of resistors, EMF, internal resistance, and Kirchhoff’s rules.
📘 Key Formulae
- I = Q/t (Current)
- V = IR (Ohm's Law)
- R = ρL/A (Resistivity Formula)
- P = VI = I²R = V²/R (Power)
- E = V + Ir (EMF with internal resistance)
- σ = 1/ρ (Conductivity)
📌 Concepts to Remember
- Electric current flows from higher to lower potential.
- Resistance increases with temperature for metals.
- Ohmic vs Non-Ohmic conductors (diodes, gases).
- Combination of resistors:
- Series: R = R₁ + R₂ + ...
- Parallel: 1/R = 1/R₁ + 1/R₂ + ...
- Kirchhoff’s Laws:
- Junction Rule: Sum of currents at junction = 0
- Loop Rule: Sum of potential difference in a closed loop = 0
🧪 Sample Problem
Q: Find the equivalent resistance of 3 resistors 2Ω, 3Ω, and 6Ω in parallel.
Solution: 1/R = 1/2 + 1/3 + 1/6 = (3+2+1)/6 = 6/6 = 1 → R = 1Ω
💡 Pro Tips
- Use sign conventions carefully in loop rule.
- Practice solving circuits using both series-parallel and Kirchhoff’s law.
- Focus on Wheatstone Bridge and Meter Bridge concepts for both JEE and CBSE.
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