Class 10 · NCERT Science

Chapter 11

Electricity

Use current, potential difference, resistance, Ohm's law, and power. Learn the ideas, see how they connect, and practise until you can choose the next step without help.

Ohm's lawResistancePower

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Study board

Quick reference
Concept 01Ohm's law
Concept 02Resistance
Concept 03Power

NCERT chapter notes

Electricity, clearly explained

Electricity in the CBSE Class 10 Science syllabus deals with electric current, potential difference, and resistance, and how these are linked by Ohm's law. The chapter builds from the idea of charges in motion to complete circuits, then to how resistors combine in series and parallel and how electric energy turns into heat and power.

Most board marks in this chapter come from Ohm's law numericals, series-and-parallel resistance problems, and the heating effect of current. Understanding the formulae and their sign-free, unit-correct application matters more than memorising definitions.

Core concepts

Key concepts and formulae

01

Electric current (I = Q/t)

Electric current is the rate of flow of charge. Its SI unit is the ampere (A); 1 A = 1 coulomb per second. By convention current flows from the positive to the negative terminal, opposite to electron flow. Current is measured by an ammeter connected in series.

02

Potential difference (V = W/Q)

Potential difference between two points is the work done to move a unit charge between them. Its SI unit is the volt (V); 1 V = 1 joule per coulomb. It is measured by a voltmeter connected in parallel across the component.

03

Ohm's law (V = IR)

At constant temperature, the current through a conductor is directly proportional to the potential difference across it, so V = IR. The V–I graph is a straight line through the origin for an ohmic conductor. Resistance R is measured in ohms (Ω).

04

Factors affecting resistance (R = ρL/A)

Resistance increases with length (R ∝ L), decreases with larger cross-sectional area (R ∝ 1/A), and depends on the material's resistivity ρ and on temperature (resistance of a metal rises with temperature).

05

Series and parallel resistors

In series the current is the same everywhere and Rs = R₁ + R₂ + R₃; the total resistance is larger than any single resistor. In parallel the voltage is the same across each branch and 1/Rp = 1/R₁ + 1/R₂ + 1/R₃; the total resistance is smaller than the smallest resistor.

06

Heating effect and electric power

Joule's law of heating gives H = I²Rt. Electric power P = VI = I²R = V²/R, measured in watts. The commercial unit of electrical energy is the kilowatt-hour (kWh); 1 kWh = 3.6 × 10⁶ J.

Exam practice

Important questions, with worked answers

Use each answer to check the method and wording—not as a paragraph to memorise.

Q1State Ohm's law. Draw the V–I graph for an ohmic conductor.

Answer

Ohm's law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across its ends (V = IR). The V–I graph is a straight line passing through the origin, whose slope gives the resistance.

Q2Why is the series arrangement not used for connecting domestic appliances in a circuit?

Answer

In series the same current flows through every appliance, so they cannot be operated at their own required currents/voltages; if one appliance fails or is switched off, the circuit breaks and all appliances stop working. Hence appliances are connected in parallel at home.

Q3Why are the coils of electric toasters and irons made of an alloy such as nichrome rather than a pure metal?

Answer

An alloy like nichrome has high resistivity (so it produces more heat), a high melting point (so it does not melt at high temperature), and does not oxidise (burn) readily when hot in air.

Q4Why is tungsten used almost exclusively for filaments of electric lamps?

Answer

Tungsten has a very high melting point (about 3380 °C) and high resistivity, so it can be heated to a high temperature to emit light without melting.

Q5An electric bulb is rated 220 V and 100 W. Calculate the current drawn and its resistance.

Answer

Current I = P/V = 100/220 ≈ 0.45 A. Resistance R = V²/P = (220)²/100 = 484 Ω.

Q6How much energy in joules is consumed when a 1000 W heater runs for 1 hour, and what is this in kWh?

Answer

Energy = P × t = 1000 W × 3600 s = 3.6 × 10⁶ J = 1 kWh (one unit of electricity).

Q7Two resistors of 4 Ω and 6 Ω are connected (a) in series and (b) in parallel. Find the equivalent resistance in each case.

Answer

(a) Series: Rs = 4 + 6 = 10 Ω. (b) Parallel: 1/Rp = 1/4 + 1/6 = 5/12, so Rp = 12/5 = 2.4 Ω.

Q8Why are copper and aluminium wires usually used for electricity transmission?

Answer

Copper and aluminium have very low resistivity, so they offer little resistance to current and lose very little energy as heat during transmission.

Fast recall

Key terms to remember

Ampere: SI unit of electric current; 1 A = 1 coulomb per second.

Volt: SI unit of potential difference; 1 V = 1 joule per coulomb.

Resistance: Property of a conductor that opposes the flow of current; measured in ohms (Ω).

Resistivity: Material property equal to the resistance of a unit-length, unit-area conductor; determines how good a conductor a material is.

Kilowatt-hour: Commercial unit of electrical energy; 1 kWh = 3.6 × 10⁶ J.

A repeatable method

How to learn Electricity properly

  1. 1

    Start with the chapter promise

    Use current, potential difference, resistance, Ohm's law, and power. Before solving, the student should be able to say what the chapter is trying to teach and which kind of problem it helps solve.

  2. 2

    Build the core vocabulary

    The important words for this chapter are Ohm's law, Resistance and Power. Eduro should make the student define each one in simple language, then use it in a question or explanation.

  3. 3

    Move from recognition to recall

    Recognition means the answer makes sense after seeing it. Recall means the student can produce the next step independently. This page is built for recall, because that is what tests reward.

  4. 4

    Close the loop with practice

    A strong study session ends with concept and diagram practice, not only reading. The student should solve, review the mistake, and then attempt a similar question before moving on.

Before the test

Where students usually lose marks

Look for the first wrong decision—not only the final wrong answer. That is the mistake worth repairing.

Mistake 1

Knowing Ohm's law only after seeing the solution

This is the most common hidden gap. The student feels confident while reading, but cannot choose the starting step alone. Eduro should ask a short diagnostic question before explaining the method.

Mistake 2

Treating Electricity as a memory chapter

Even memory-heavy chapters need reasoning. A memorised line becomes fragile when the question changes. The student should explain why the answer works, not only what the answer is.

Mistake 3

Skipping the checking step

concept-to-example gap usually survives because the student finishes the answer and moves on. Eduro should make review part of the answer: what was asked, what was used, and whether the final response fits.

Try it with Eduro

Practice that builds real confidence

Say it naturally, as you would to a patient teacher. Each prompt below is designed to make understanding visible.

Prompt 1

Ask Eduro to explain Electricity through Ohm's law before showing any solved answer.

Prompt 2

Create five questions that separately test Ohm's law, Resistance and Power.

Prompt 3

Give one wrong answer from Electricity and ask the student to find the first incorrect step.

Prompt 4

End with a mixed mini-test where Eduro does not reveal which skill is being tested.

For parents

A better way to ask, “Is the chapter done?”

For Class 10 Science, a good sign is not that the child says 'Electricity is done.' A better sign is that they can explain Ohm's law, solve one fresh question, and correct one mistake without panic.

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Reviewed for the 2025-26 CBSE/NCERT study cycle

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Quick help

Common questions

How can I study Electricity for NCERT Class 10?

Start with the NCERT examples, understand the key ideas in Ohm's law, Resistance, Power, then practice exercise questions and ask Eduro where you get stuck.

Can Eduro help with Electricity?

Yes. Eduro can explain Electricity step by step, answer follow-up doubts, and help students practice related Science questions.