A current of 4·0 A flows through a wire of length 1 m and cross-sectional area 1·0\ mm², when potential difference of 2 V is applied across its ends. Calculate the resistivity of the material of the wire.

PhysicsCBSE Class 12 · Board exam 2026, set 55/5/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2026: question 17(b)

Set in the CBSE Class 12 board exam of 2026, paper 55/5/1, section B, question 17(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q17(b) · 2 marks · Very short answerCurrent Electricity

A current of 4·0 A flows through a wire of length 1 m and cross-sectional area $1 \cdot 0 mm^{2}$ , when potential difference of 2 V is applied across its ends.
Calculate the resistivity of the material of the wire.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

First find the resistance from V and I.

Hint 2

Relate resistance to resistivity: $R = ρl / A$ .

Hint 3

Convert 1 mm² to m² ( $1 0^{- 6}$ m²).

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

Resistance of the wire: $R = \frac{V}{I} = \frac{2}{4.0} = 0.5 Ω$
1 mark
From $R = \frac{ρl}{A}$ : $ρ = \frac{R A}{l} = \frac{0.5 \times 1.0 \times 1 0 ^{- 6}}{1} = 5 \times 1 0^{- 7} Ω m$
1 mark

Answer: ρ = 5 × 10^-7 Ω m

Where the marks are

Finds R = 0.5 Ω using Ohm's law (1 mark)
Uses $ρ = R A / l$ with A in m² to get $5 \times 1 0^{- 7} Ω$ m (1 mark)

Revise the chapter

Chapter: Current Electricity (notes, formulas, where marks are lost and every past question)
Topic: Drift Velocity, Mobility and Resistivity

Practise this chapterBoard-style questions from Current Electricity, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 55/5/1: every question, by section.

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CBSE Class 12 Physics 2026: question 17(b)

Hints

Step-by-step solution

Revise the chapter

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