- Current, I = Q/t (ampere, A); Potential difference, V = W/Q (volt, V)
- Ohm’s Law: V = IR, at constant temperature
- Resistance: R = ρL/A — directly proportional to length, inversely proportional to cross-sectional area, ρ = resistivity (material property, unit Ω m)
- Series combination: R_s = R₁+R₂+R₃+…; same current through each, voltages add
- Parallel combination: 1/R_p = 1/R₁+1/R₂+1/R₃+…; same voltage across each, currents add
- Electric power: P = VI = I²R = V²/R (watt, W)
- Electrical energy: E = Pt; commercial unit = 1 kWh = 3.6×10⁶ J
- Heating effect (Joule’s law): H = I²Rt
- Ammeter: connected in series, near-zero resistance. Voltmeter: connected in parallel, very high resistance.
- Tungsten (high melting point, doesn’t oxidise) → bulb filaments. Alloys like Nichrome (high resistivity, high melting point) → heating elements.
- Series wiring is not used domestically: one break stops everything, and all appliances would be forced to share one current value.
- This chapter is now Chapter 11 in the 2026-27 rationalised book (was Chapter 12 pre-2023).
See the full Solutions post · Extra Questions / HOTS · Class 10 Science Formulas Handbook
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