Chapter 11 — Electricity

Chapter 11 of the Class 10 Science NCERT textbook, "Electricity", covers the flow of electric charge through conductors, governed by Ohm's law (V = IR), resistance, series and parallel circuits, Joule's heating effect (H = I²Rt), and electric power (P = VI).

• Current, voltage, and Ohm's law — Electric current is the rate of charge flow, driven by a potential difference across a circuit. Ohm's law ties them together as V = IR, showing that resistance controls how much current a given voltage pushes through.
• What resistance depends on — A conductor's resistance grows with its length and falls with its cross-sectional area, and depends on the material's resistivity. This is why thin, long, or high-resistivity wires resist current more than short, thick ones.
• Combining resistors and heating effects — Resistors in series add directly, while in parallel their reciprocals add. The heating effect, given by Joule's law, and electric power measured in watts explain how heaters, bulbs, and fuses work and how energy is billed.

1. 01Electric current I = Q/t is measured in amperes (A); 1 coulomb of charge equals the charge of approximately 6 × 10¹⁸ electrons.
2. 02Ohm's law: potential difference V across a conductor is directly proportional to current I at constant temperature, expressed as V = IR.
3. 03Resistance R = ρl/A; resistivity ρ (in Ω m) depends on the material — metals have resistivity 10⁻⁸ to 10⁻⁶ Ω m, insulators 10¹² to 10¹⁷ Ω m.
4. 04In a series circuit, equivalent resistance Rs = R1 + R2 + R3 and the same current flows through all resistors; in a parallel circuit, 1/Rp = 1/R1 + 1/R2 + 1/R3 and the same potential difference appears across each resistor.
5. 05Joule's law of heating: H = I²Rt — heat produced is proportional to the square of current, resistance, and time; this principle powers electric heaters, irons, and fuses.
6. 06Electric power P = VI = I²R = V²/R in watts (W); commercial electrical energy is measured in kilowatt hours (1 kWh = 3.6 × 10⁶ J).