Skip to content

Answer the following. (Science 2025 31/1/1 Q33)

questionbuddy.in/q/cbse-10-science-2025-31-1-1-q33

ScienceCBSE Class 10 · Board exam 2025, set 31/1/1 · 3 marks · Short answer

CBSE Class 10 Science 2025: question 33

Set in the CBSE Class 10 board exam of 2025, paper 31/1/1, section C, question 33, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q33 · 3 marks · Short answerElectricity

Answer the following.

  1. (a)

    Write the relationship between resistivity and resistance of a cylindrical conductor of length and area of cross-section . Hence derive the SI unit of resistivity.

    0 marks
  2. (b)

    Why are alloys used in electrical heating devices?

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/1/1.

Hints

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

Hint 1

How does R change with length and with area of cross-section?

Hint 2

Make ρ the subject, then substitute the units of R, A and l.

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. (a) Resistance of a uniform cylindrical conductor: , where is the resistivity of the material.

    1 mark

  2. (a) Rearranging:

    ½ mark

  3. (a) SI unit of (ohm metre).

    ½ mark

  4. (b) Alloys are used in heating devices because their resistivity is higher than that of pure metals, so they produce more heat. They also do not oxidise (burn) readily at high temperatures.

    1 mark

Answer: (a) R = ρl/A, so ρ = RA/l; SI unit Ω m; (b) high resistivity and they do not oxidise readily at high temperatures

Where the marks are

  • Writes R = ρl/A (1 mark)
  • Rearranges to ρ = RA/l (½ mark)
  • Derives the unit Ω m (½ mark)
  • High resistivity / do not oxidise at high temperature (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Electricity, one at a time, marked against the answer key and marking points.Back to the full paper2025 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.