CBSE Class 10 Science — Electricity | Important Concept-Based Questions & Exam Tips

CBSE Class 10 Science: Electricity — Concept-Based Questions & Smart Revision

CBSE Class 10 Science: Electricity — Important Concept-Based Questions

Clear concepts • Exam-style problems • Smart revision plan — designed for Class 10 board success

Chapter Focus: Electricity

What you’ll get in this article

Concise concept explanations that CBSE loves
20+ exam-like concept questions with model answers
Stepwise solved numericals, quick formulas and a 7-day revision plan

Quick read • Print-ready • Blogger HTML

Overview: Electricity in Class 10 covers electric current, potential difference, resistance and resistivity, Ohm's law, series/parallel combinations, electric power, and practical experiments (V–I graph). The board expects students to demonstrate concept clarity, correct formula usage, clear units and neat diagrams. This article gives focused concept questions with model answers, solved numericals and practical tips to score high.

Essential concepts (short & sharp)

Current & Potential Difference

Current (I) is the rate of flow of charge. Unit: ampere (A). Potential difference (V) between two points is the work done to move a unit charge between those points. Unit: volt (V).

Conventional current flows from positive to negative.
Charge (Q) and current: Q = I × t.

Resistance & Resistivity

Resistance (R) is opposition to current. Unit: ohm (Ω). Resistivity (ρ) is a material property and R = ρL/A.

R ∝ L (direct), R ∝ 1/A (inverse).
Temperature affects resistivity (metals: ρ increases with temperature).

Key formulas — keep this on one index card

Ohm’s law: V = I R
Resistance: R = ρ L / A
Series: R_eq = R1 + R2 + …
Parallel: 1/R_eq = 1/R1 + 1/R2 + …
Power: P = V I = I² R = V² / R
Heating/Energy: E = P t = I² R t

Concept-based questions (model answers)

Q1. State Ohm’s law. Mention a limitation.

Answer: Ohm’s law: At constant physical conditions (e.g., constant temperature), the potential difference across a conductor is directly proportional to the current through it (V ∝ I), or V = IR. Limitation: It applies to ohmic conductors only; non-ohmic elements (like diodes, filament bulbs at varying temperature) do not follow a linear V–I relationship.

Q2. How does resistance change when length is doubled and cross-sectional area halved?

Answer: R = ρL/A. If L → 2L and A → A/2, R' = ρ(2L)/(A/2) = 4ρL/A = 4R. So resistance becomes four times larger.

Q3. Why is equivalent resistance in parallel less than the smallest resistor?

Answer: Parallel branches provide additional current paths; for the same voltage more total current flows. Since R_eq = V / I_total and I_total increases, R_eq decreases — always less than the smallest branch resistance.

Q4. Explain why copper is preferred in house wiring over iron.

Answer: Copper has lower resistivity (smaller R for same dimensions), higher ductility (easier to draw into wires), and better corrosion resistance compared to iron. This reduces heating losses and improves safety.

Q5. A filament lamp shows a non-linear V–I graph. Explain.

Answer: As current passes, filament heats up, increasing resistance; hence V–I relation becomes non-linear. At higher V, resistance increases, making graph curve away from straight line.

Solved numericals (clear stepwise answers)

Numerical 1. A 9 V battery is connected to a 18 Ω resistor. Find current and power dissipated.

Solution: I = V/R = 9/18 = 0.5 A. Power P = V × I = 9 × 0.5 = 4.5 W (or P = I²R = 0.5² × 18 = 4.5 W).

Numerical 2. Three resistors 4 Ω, 6 Ω and 12 Ω are connected: 4 Ω and 6 Ω in series, that combination in parallel with 12 Ω. Find equivalent resistance.

Solution: Series: R_s = 4 + 6 = 10 Ω. Now parallel with 12 Ω: 1/R_eq = 1/10 + 1/12 = (6+5)/60 = 11/60 ⇒ R_eq = 60/11 ≈ 5.455 Ω.

Numerical 3. A toaster rated 1200 W runs on 240 V. Find resistance and current.

Solution: P = V²/R ⇒ R = V²/P = (240²)/1200 = 57600/1200 = 48 Ω. Current I = P/V = 1200/240 = 5 A.

20 Rapid practice questions (use for timed drills)

Define current. Give SI unit.
What is potential difference? Unit?
Write Ohm’s law and its SI units.
State relation between resistance and resistivity.
How does temperature affect resistance of metals?
Find R_eq of two 10 Ω resistors in parallel.
Why is earthing important in electrical installations?
Express power in three alternative forms.
How to experimentally verify Ohm’s law? (brief)
Why is platinum used for standard resistors at high temperature?
Explain why long thin wire has more resistance than a short thick one.
What is the unit of resistivity?
When are resistors said to be in series?
Why is fuse placed in live wire?
Write formula for energy dissipated (heating) in time t.
How to reduce power loss during transmission?
State Kirchhoff’s loop rule in words.
What is meant by non-ohmic conductor? Give example.
How is current affected if voltage is doubled across same resistance?
Why do conductors heat up on heavy current?

One-page summary table (handy for last-minute)

Topic	Formula/Note	Exam Hint
Ohm's law	V = IR	Check units & linearity on V–I graph
Resistance	R = ρL/A	Note L & A changes — use ratios
Power	P = VI = I²R = V²/R	Choose form to cancel unknown
Energy	E = P t = I² R t	Convert time to seconds if J required
Series/Parallel	R_series = ΣR; 1/R_par = Σ(1/R)	Label current/voltage on diagrams

Exam strategy — present answers that get marks

          Write definitions first: Short, textbook-correct lines (units included).
Label diagrams (e.g., circuit with battery, ammeter, voltmeter) — diagrams earn marks.
Show steps: Use formula → substitute values → compute → write final answer with units.
Time management: Solve 2–3 numericals first, then concept questions—numericals often take longer.

        

Common mistakes and how to avoid them

Forgetting to convert mA to A (1000 mA = 1 A).
Using P = VI without matching units (V in volts, I in amperes).
Not simplifying circuit before calculation — reduce series/parallel groups first.
Mixing up where fuse should be placed — always in live wire; explain reason briefly in answers.

Practical tips for school experiments

When plotting V–I graph: take several readings, maintain temperature as constant as possible, use correct polarity, and draw best-fit straight line for ohmic conductor. For filament lamp expect non-linear curve — discuss heating effect in conclusion.

Why practice concept questions?

Concept-based questions test understanding, not memorization. Examiners reward answers that show reasoning sentences like "Because resistance increases with temperature, current decreases for same V", or "Equivalent resistance in parallel is less because additional paths lower net opposition". Short, precise reasoning combined with correct calculation yields maximum marks.

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