CBSE Class 10 Science: Electricity — Ohm's Law & Circuits Notes 2026

Electric Current and Potential Difference

• Current I = Q/t; unit ampere (A); measured by ammeter (series connection)
• Potential difference V = W/Q; unit volt (V); measured by voltmeter (parallel connection)
• Conventional current flows from + to −; electron flow is opposite

Ohm's Law

• V ∝ I at constant temperature; V = IR; R = V/I (ohm = V/A)
• Ohmic conductor: straight V–I graph through origin; non-ohmic: filament lamp (R increases with temperature)
• CBSE: distinguish ohmic/non-ohmic conductors with V-I graphs

Resistance — Factors

• R = ρL/A; resistance increases with length, decreases with larger cross-sectional area
• Resistivity ρ is a property of material and temperature; metals: ρ increases with temperature
• Series connection: R_total = R₁ + R₂; parallel: 1/R_total = 1/R₁ + 1/R₂

Electric Power

• P = VI = I²R = V²/R; unit watt (W)
• Electric energy = P × t; commercial unit kWh; 1 kWh = 3.6 × 10⁶ J
• Electricity bill: number of units = (wattage × hours) / 1000

Heating Effect of Current (Joule Heating)

• H = I²Rt; heat increases with square of current — basis of heater, electric iron, toaster
• Fuse: thin wire with low melting point placed in live wire; melts if current exceeds limit
• MCB (Miniature Circuit Breaker): resettable device; safer than fuse

Household Electric Circuits

• Live wire (red/brown), neutral (black/blue), earth wire (green/yellow)
• Appliances connected in parallel: each gets full 230 V; individual switches work independently
• Power factor and efficiency not required for Class 10 CBSE; focus on practical circuit understanding

CBSE Exam Numericals — Electricity

• Three resistors 5Ω, 10Ω, 15Ω in parallel; find total resistance and total current at 12 V
• A 100W bulb works for 5 hours daily for 30 days; calculate cost at ₹5/unit
• Find current through circuit; find heat produced in resistor in given time