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NCERT Class 10 Science Chapter 11, Electricity, explained simply

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Electricity is Chapter 11 of the NCERT Class 10 Science textbook (Reprint 2026-27). Almost every question comes down to a handful of formulas and two kinds of circuit. This guide explains each idea in plain words, works through the question types the CBSE sample paper uses with our own numbers, and ends with a self-check and a way to test an AI's answer.

Keep the textbook open next to it. Our explanations and examples are our own; the textbook is the authority.

How much it counts in the board exam

CBSE's Class 10 Science curriculum for 2026-27 puts this chapter in Unit IV, Effects of Current, worth 13 of the 80 theory marks, together with Magnetic Effects of Electric Current. Within the unit, the motor, electromagnetic induction and the electric generator are assessed only in school, not in the year-end paper.

The 2026-27 sample paper (Science 086) asks Electricity in three places, all in the Physics section:

QuestionMarksWhat it asks
Q311The current drawn by an appliance from its power rating and voltage
Q342Either Joule's law of heating, and what happens to the heat when the resistance doubles; or what resistivity is, and why it belongs to the material and not to the wire's size
Q373A circuit of resistors on a 15 V battery: the total current, and the potential difference between two points

That is 6 marks for Electricity. Magnetic Effects takes the other 7 (Q36 and Q38).

1. Current, charge and potential difference (sections 11.1 to 11.3)

Worked: a current of 0.2 A flows for 5 minutes. Charge = I × t = 0.2 A × 300 s = 60 C. Moving 3 C across a 9 V battery takes W = V × Q = 9 V × 3 C = 27 J.

2. Ohm's law and resistance (section 11.4)

For a metal wire kept at the same temperature, doubling the current doubles the voltage across it: V and I rise in step. That is Ohm's law: V = IR, where R is the wire's resistance in ohms (Ω).

Read it three ways:

A V-I graph for such a wire is a straight line through the origin, and its slope is R.

Worked: 12 V across a 48 Ω resistor drives I = 12/48 = 0.25 A.

3. What resistance depends on: resistivity (section 11.5)

A uniform wire's resistance grows with its length (l) and falls as its cross-section area (A) grows: R = ρl/A. The constant ρ (rho) is the material's resistivity, in Ω m.

Resistivity belongs to the material, not to one wire: cut a copper wire shorter or use a thicker one, and R changes, but ρ for copper stays the same. That is the idea behind the sample paper's Q34, option B.

From the book's table: metals such as copper and silver have very low resistivity, alloys such as nichrome much higher, and insulators such as glass and rubber higher still. That explains three uses:

Worked: a nichrome wire (ρ = 100 × 10⁻⁶ Ω m) is 2 m long with a cross-section of 1 mm² = 1 × 10⁻⁶ m². R = ρl/A = (100 × 10⁻⁶ × 2) / (1 × 10⁻⁶) = 200 Ω.

The scaling trick: if the same material is made twice as long and half as thick in area, R = ρ(2l)/(A/2) = 4ρl/A, so the resistance becomes 4 times as much. You do not need numbers, only the ratios.

4. Resistors in series and in parallel (section 11.6)

Series (end to end)Parallel (side by side)
CurrentThe same through every resistorSplits: I = I₁ + I₂ + I₃
Potential differenceSplits: V = V₁ + V₂ + V₃The same across every resistor
Total resistanceRs = R₁ + R₂ + R₃, bigger than the biggest1/Rp = 1/R₁ + 1/R₂ + 1/R₃, smaller than the smallest

Worked, series: 2 Ω, 4 Ω and 6 Ω in series on a 6 V battery. Rs = 12 Ω, so I = 6/12 = 0.5 A through each. The voltages are 0.5 × 2 = 1 V, 0.5 × 4 = 2 V and 0.5 × 6 = 3 V, which add up to the battery's 6 V.

Worked, parallel: 6 Ω and 3 Ω in parallel on a 6 V battery. Each gets the full 6 V, so the currents are 6/6 = 1 A and 6/3 = 2 A, and the battery gives 3 A. Then 1/Rp = 1/6 + 1/3 = 1/2, so Rp = 2 Ω (check: 6 V / 3 A = 2 Ω).

Worked, mixed (like the sample paper's Q37): two 4 Ω resistors in parallel, and that pair in series with a 3 Ω resistor, on a 10 V battery.

  1. Replace the parallel pair first: 1/R = 1/4 + 1/4 = 1/2, so R = 2 Ω.
  2. Now it is a simple series circuit: 2 Ω + 3 Ω = 5 Ω.
  3. Total current: I = 10/5 = 2 A.
  4. Potential difference across the parallel pair: 2 A × 2 Ω = 4 V, so each 4 Ω resistor carries 4/4 = 1 A.

The book also gives the reason houses are wired in parallel: each appliance gets the full mains voltage and can draw the current it needs, and one appliance failing does not switch off the others.

5. The heating effect, power and energy (sections 11.7 and 11.8)

In a circuit of resistors only, all the energy the source supplies turns into heat:

H = VIt = I²Rt (Joule's law of heating)

So the heat is proportional to the square of the current, to the resistance, and to the time. Double the resistance with the same current, and the heat doubles (that is Q34, option A).

Electric power is the rate of using energy:

P = VI = I²R = V²/R, in watts (W).

The bill counts energy in kilowatt hours ("units"): 1 kW h = 3.6 × 10⁶ J.

Worked, heating: 2 A through a 10 Ω resistor for one minute gives H = 2² × 10 × 60 = 2400 J.

Worked, power: an 1100 W kettle on a 220 V supply draws I = P/V = 1100/220 = 5 A, and its element has R = V²/P = 220²/1100 = 44 Ω.

Worked, the sample paper's Q31 type: an appliance rated 1000 W on 250 V draws 1000/250 = 4 A.

Worked, energy and cost: a 1.5 kW air conditioner runs 6 hours a day for 30 days: 1.5 × 6 × 30 = 270 kW h (270 units). At an example rate of ₹7 a unit, that is ₹1,890.

Fuses use the heating effect on purpose. A fuse wire in series with an appliance melts if the current gets too high. Choose the next rating above the normal current: a 2000 W heater on 220 V draws 2000/220 ≈ 9.1 A, so it needs a 10 A fuse, not a 5 A one.

Safety: mains electricity (220 V) can kill. Never open a plug, switchboard, fuse box or appliance, and never change a fuse or wire yourself: that is a job for an adult electrician. Try circuits only with torch cells, as the book's activities do.

6. Mistakes that cost marks

  1. Forgetting to convert units. Minutes to seconds, mm² to m² (1 mm² = 10⁻⁶ m²), watts to kilowatts. Most wrong numerical answers in this chapter are unit slips.
  2. Stopping at 1/Rp. The parallel formula gives the reciprocal. If 1/Rp = 1/2, the answer is 2 Ω, not 0.5 Ω.
  3. Using the total voltage on one series resistor. In series, each resistor gets only its share (V = IR for that resistor).
  4. Mixing up where meters go. Ammeter in series, voltmeter in parallel.
  5. A total that cannot be right. A series total must be bigger than the biggest resistor; a parallel total must be smaller than the smallest. Check this before you move on.

7. Self-check: 6 questions with answers

Try them on paper first. Answers are below.

  1. A charge of 120 C flows through a wire in 1 minute. What is the current?
  2. A torch bulb draws 0.3 A from a 4.5 V battery. What is its resistance?
  3. Resistors of 3 Ω, 6 Ω and 9 Ω are in series on a 9 V battery. Find the current and the potential difference across the 6 Ω resistor.
  4. The same three resistors are joined in parallel instead. What is their total resistance?
  5. A second wire of the same material is twice as long and has twice the cross-section area. Compare its resistance with the first wire's.
  6. A 60 W bulb is on for 5 hours a day for 30 days. How many units (kW h) does it use?

Answers: 1) I = Q/t = 120 C / 60 s = 2 A. 2) R = V/I = 4.5/0.3 = 15 Ω. 3) Rs = 3 + 6 + 9 = 18 Ω, so I = 9/18 = 0.5 A, and the 6 Ω resistor gets 0.5 × 6 = 3 V. 4) 1/Rp = 1/3 + 1/6 + 1/9 = 6/18 + 3/18 + 2/18 = 11/18, so Rp = 18/11 ≈ 1.64 Ω. It is smaller than 3 Ω, the smallest, as it must be. 5) The same. R = ρ(2l)/(2A) = ρl/A: doubling both length and area leaves the resistance unchanged. 6) 60 W × 5 h × 30 = 9000 W h = 9 kW h.

8. How to check an AI's answer for this chapter

Chatbots are fast with formulas and still slip on numbers. These checks take a minute:

More on using AI well: how to use ChatGPT for homework without cheating yourself.

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Sources

All checked on 20 October 2026.

The formulas, section numbers, the resistivity values and the question types are from the documents above. All explanations, worked examples and self-check questions on this page are our own; every number was checked by calculation.

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