Last Updated: May 2026
CBSE Class 10 Science Chapter 12 — Electricity contributes 5-6 marks on the CBSE Board exam every year, with at least one 3-mark numerical and one 5-mark circuit-based question. Combined with Chapter 13 (Magnetic Effects of Electric Current), the electricity block forms the highest-weight Physics topic in Class 10. This guide covers complete NCERT notes, all standard formulae, common question types, and 25 board-style MCQs.
Quick Facts: CBSE Class 10 Electricity 2026-27
| Aspect | Detail |
|---|---|
| NCERT chapter | Class 10 Science, Chapter 12 |
| Marks weightage | 5-6 (Physics block: 27 marks of 80) |
| Difficulty | Moderate |
| Question types | 1-mark MCQ, 2-mark short, 3-mark numerical, 5-mark circuit problem |
| Most-tested zones | Ohm’s law, series-parallel resistors, electrical power, heating effect |
Key Concepts
1. Electric Current
- Current I = Q/t — rate of flow of charge.
- SI unit: ampere (A) = 1 coulomb/sec.
- Conventional current direction: positive to negative (opposite to electron flow).
2. Potential Difference (Voltage)
- V = W/Q — work done per unit charge.
- SI unit: volt (V) = 1 joule/coulomb.
- Voltmeter: measures V; connected in parallel.
3. Ohm’s Law
- V = IR, where R is resistance.
- SI unit of resistance: ohm (Ω) = 1 V/A.
- Ammeter: measures I; connected in series.
4. Resistance and Resistivity
- R = ρL/A, where ρ is resistivity (specific resistance).
- SI unit of ρ: Ω·m.
- Conductors: low ρ (Cu = 1.7×10⁻⁸ Ω·m); insulators: very high ρ.
- R increases with temperature in metals.
Series and Parallel Circuits
| Property | Series | Parallel |
|---|---|---|
| Same in all components | Current (I) | Voltage (V) |
| Net resistance | R = R₁ + R₂ + R₃ | 1/R = 1/R₁ + 1/R₂ + 1/R₃ |
| Voltage divides | V = V₁ + V₂ + … | Same across all |
| Current divides | Same in all | I = I₁ + I₂ + … |
| Used in | Decorative bulbs | Household wiring |
Memory tip: Net resistance in parallel is always less than the smallest individual resistance.
Electric Power and Heating Effect (HIGH-YIELD)
- Power P = VI = I²R = V²/R.
- SI unit: watt (W) = 1 J/s.
- Energy E = Pt; commercial unit: 1 kWh = 1 unit = 3.6 × 10⁶ J.
- Joule’s law of heating: H = I²Rt — used in heaters, geysers, electric irons.
Worked Example — 3-Mark Numerical (Standard Board Pattern)
Q. Three resistors of 5 Ω, 10 Ω and 15 Ω are connected in parallel. The combination is connected to a 6 V battery. Find the total current drawn from the battery.
Solution: 1/R = 1/5 + 1/10 + 1/15 = 6/30 + 3/30 + 2/30 = 11/30 → R = 30/11 ≈ 2.73 Ω.
I = V/R = 6/(30/11) = 66/30 = 2.2 A.
Worked Example — 5-Mark Circuit Problem
Q. A circuit has a 12 V battery, a 4 Ω resistor in series, and two parallel resistors (8 Ω and 8 Ω) at the end. Calculate (i) total resistance, (ii) total current, (iii) power dissipated by each resistor.
Solution:
- Rparallel = (8 × 8)/(8 + 8) = 4 Ω. Rtotal = 4 + 4 = 8 Ω.
- I = 12/8 = 1.5 A.
- Voltage across 4 Ω resistor: V = 1.5 × 4 = 6 V; P = 9 W.
Voltage across parallel block: 12 − 6 = 6 V; current through each 8 Ω = 6/8 = 0.75 A; P each = 0.75 × 6 = 4.5 W.
Common Misconceptions Boards Test
- Voltmeter in parallel, ammeter in series — reversed connections destroy the meter.
- Resistance is NOT same as resistivity — R depends on shape, ρ does not.
- Bulb’s resistance increases with temperature — hot resistance > cold resistance.
- kWh is energy, not power. Convert to joules carefully.
- Open vs short circuit: Short circuit has near-zero resistance and infinite current — fuse breaks.
Application — Why Household Wiring is in Parallel
- Each appliance gets the same voltage (220 V).
- If one device fails, others continue working.
- Multiple branches share the load.
- Series wiring would mean one bulb burning would disconnect everything.
FAQ — CBSE Class 10 Electricity 2026-27
Q1. State Ohm’s law.
Q2. Why is the filament of an electric bulb made of tungsten?
Q3. What is 1 unit of electricity?
Q4. Why are series circuits not used in domestic wiring?
Q5. Define electric power and write its SI unit.
Practice MCQs
Quiz data missing.
Related Reading
- Class 10 Acids, Bases & Salts
- Class 10 Light: Reflection & Refraction
- Class 10 How Do Organisms Reproduce
- Class 10 Maths — Triangles
- CBSE Class 10 Mock Test
Bottom line: Master Ohm’s law, series-parallel resistance formulae, and electric power equations — that’s 90% of your CBSE board electricity questions. Solve every NCERT example and at least 30 board-style numericals to be exam-ready.
