Ch 12 covers electric current, potential difference, Ohm's law, resistance, series and parallel combinations, electric power, and energy — essential for understanding household circuits.
Electric current I = Q/t (charge per second, unit: ampere A). Potential difference V (voltage, unit: volt V) drives current. Ohm's law: V = IR (at constant temperature). Resistance R (unit: ohm Ω) depends on: length (R ∝ L), cross-section (R ∝ 1/A), material (resistivity ρ), temperature. R = ρL/A.
Series: components connected end-to-end. Same current through all. R_total = R₁ + R₂ + R₃. Voltage divides. One component fails → circuit breaks. Parallel: components connected across same two points. Same voltage across all. 1/R_total = 1/R₁ + 1/R₂ + 1/R₃. Current divides. One component fails → others still work (household wiring).
Electric power P = VI = I²R = V²/R (unit: watt W). Energy consumed E = P × t. Commercial unit: kWh (1 unit). 1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J. Electrical fuse: thin wire that melts if current exceeds safe limit, breaking the circuit.
Download: https://ncert.nic.in/textbook/pdf/jesc112.pdf | Complete book: https://ncert.nic.in/textbook/pdf/jesc1ps.zip
Parallel connection ensures: (1) each appliance gets the full 220V mains voltage, (2) turning off one appliance doesn't affect others, (3) total resistance decreases allowing more current from the source, (4) if one fuse blows, others keep working. Series connection would divide voltage and break all appliances if one fails.
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