Quick Revision

Ohm's Law states that the electric current flowing through a conductor is directly proportional to the potential difference across its ends, provided the temperature and other physical conditions remain constant. V = IR, where V = potential difference (volts), I = current (amperes), R = resistance (ohms). The V-I graph for an ohmic conductor is a straight line through the origin.

The SI unit of electric current is Ampere (A), named after André-Marie Ampère. 1 Ampere = 1 Coulomb per second (1 A = 1 C/s). It measures the rate of flow of charge.

For parallel combination: 1/Rₚ = 1/R₁ + 1/R₂ + 1/R₃ 1/Rₚ = 1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 6/6 = 1 Rₚ = 1 Ω The equivalent resistance in parallel is always less than the smallest individual resistance. Here 1 Ω < 2 Ω (smallest). In parallel, same potential difference across all resistors but current divides.

Electric power P = VI = I²R = V²/R, where P = power (watts), V = potential difference (volts), I = current (amperes), R = resistance (ohms). 1 Watt = 1 Volt × 1 Ampere. The commercial unit of energy is kilowatt-hour (kWh): 1 kWh = 3.6 × 10⁶ J.

Rate of heat production = Power = I²R = (15)² × 8 = 225 × 8 = 1800 W = 1.8 kW. Using Joule's law of heating: H = I²Rt, so rate = H/t = I²R = 1800 J/s = 1800 W.