ICSE Class 10 Physics: Electricity — Current, Resistance Notes 2026

Electric Current and Charge

• Current I = Q/t; SI unit ampere (A); conventional current direction opposite to electron flow
• Conductors, semiconductors and insulators; free electron model
• Ammeter: connected in series; voltmeter: in parallel

Ohm's Law and Resistance

• V = IR; valid for metallic conductors at constant temperature
• Resistance R = ρL/A; resistivity ρ depends on material and temperature
• V–I graph: straight line through origin for ohmic conductor

Combination of Resistors

• Series: R_total = R₁ + R₂ + …; same current, voltages add
• Parallel: 1/R_total = 1/R₁ + 1/R₂ + …; same voltage, currents add
• Equivalent resistance problems with mixed series-parallel networks

Electrical Power and Energy

• P = VI = I²R = V²/R; SI unit watt (W)
• Electrical energy E = Pt; commercial unit kWh; 1 kWh = 3.6 × 10⁶ J
• Electricity bill calculation: units consumed × rate per unit

Heating Effect of Current

• Joule's law: H = I²Rt; heat produced proportional to square of current
• Applications: electric iron, heater, fuse (low melting point wire)
• Fuse: thin wire that melts when current exceeds rated value; placed in live wire

Household Wiring and Safety

• Three-wire system: live (red/brown), neutral (black/blue), earth (green/yellow)
• MCB vs. fuse; ELCB (Earth Leakage Circuit Breaker) for personal safety
• Short circuit and overloading: causes, effects, prevention

Numericals — Electricity

• Find total resistance, current and potential drop across each resistor in mixed circuit
• Calculate power dissipated in a resistor; energy in kWh over 30 days
• Fuse selection: choose correct rating for appliance of known wattage