Skip to content

A. State the relationsh… (Class 10 Science SQP 2024-25, Q32)

questionbuddy.in/q/cbse-10-science-2024-25-sqp-q32-relationship-between-resistance-wire-length

ScienceCBSE Class 10 · Sample paper, session 2024-25 · 3 marks · Short answer

CBSE Class 10 Science sample paper 2024-25: question 32

From the official CBSE sample question paper for 2024-25, section C, question 32, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q32 · 3 marks · Short answerElectricity

A. State the relationship between the resistance R of a wire to its length l and cross sectional area A. Use the mathematical symbols to arrive at the final formula.
B. Using the formula define the resistivity of a material.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

How does resistance change if you double the length? If you double the thickness?

Hint 2

Combine the two proportionalities and introduce a constant.

Hint 3

Make ρ the subject and choose unit values for l and A.

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. The resistance of a wire is directly proportional to its length:

    ½ mark

  2. It is inversely proportional to its area of cross-section: . Combining, .

    ½ mark

  3. So , where is a constant called the resistivity of the material.

    ½ mark

  4. B. Rearranging, . If m and , then .

    1 mark

  5. Resistivity is the resistance of a wire of the material of length 1 m and cross-sectional area 1 m². Its SI unit is Ω m.

    ½ mark

Answer: R = ρl/A; resistivity is the resistance of a 1 m long conductor of the material with 1 m² cross-sectional area (unit Ω m).

Where the marks are

  • and (1 mark)
  • Final formula (0.5 mark)
  • Rearranges to and substitutes l = 1 m, A = 1 m² (1 mark)
  • Correct definition of resistivity (0.5 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 paperSample paper 2024-25: 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.