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Answer the following. (Science 2026 31/1/1 Q39a)

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ScienceCBSE Class 10 · Board exam 2026, set 31/1/1 · 5 marks · Long answer

CBSE Class 10 Science 2026: question 39(a)

Set in the CBSE Class 10 board exam of 2026, paper 31/1/1, section C, question 39(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q39(a) · 5 marks · Long answerElectricity

Answer the following.

  1. (i)

    Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why?

    0 marks
  2. (ii)

    Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why?

    0 marks
  3. (iii)

    Define the S.I. unit of electric current.

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/1/1.

Hints

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

Hint 1

Write the formula linking R, ρ, l and A, and see which quantities depend on the shape of the wire.

Hint 2

For heating appliances, think about how much heat the element must produce and what happens to it at high temperature.

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.

  1. (i) Resistance is . It is directly proportional to the length and inversely proportional to the area of cross-section . So changing or changes .

    1 mark

  2. (i) Resistivity is a characteristic property of the material (at a given temperature). It does not depend on the dimensions of the conductor, so it does not change.

    1 mark

  3. (ii) An alloy has a higher resistivity than its constituent pure metals, so it produces more heat for the same current.

    1 mark

  4. (ii) Alloys also do not oxidise (burn) readily at high temperatures. This makes them ideal for heating elements such as those in toasters and irons.

    1 mark

  5. (iii) The SI unit of electric current is the ampere (A). One ampere is the current when 1 coulomb of charge flows through a cross-section of a conductor in 1 second: .

    1 mark

Answer: (i) R = ρl/A depends on l and A, while ρ is a property of the material only; (ii) alloys have high resistivity and do not oxidise at high temperature; (iii) 1 A = flow of 1 C of charge per second

Where the marks are

  • (i) R depends on length and area via (1 mark)
  • (i) Resistivity is a characteristic of the material, so unchanged (1 mark)
  • (ii) Higher resistivity of alloys / do not oxidise readily at high temperature (2 marks)
  • (iii) 1 ampere = 1 coulomb per second (1 mark)

Revise the chapter

  • Chapter: Electricity (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Electricity, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/1/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.