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Three students Shweta, Ayesha… (Class 10 Science 2026, Q38)

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ScienceCBSE Class 10 · Board exam 2026, set 31/5/1 · 4 marks · Long answer

CBSE Class 10 Science 2026: question 38

Set in the CBSE Class 10 board exam of 2026, paper 31/5/1, section C, question 38, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q38 · 4 marks · Long answerCompetency-basedElectricity

Three students Shweta, Ayesha and Samridhi were performing an experiment to understand the factors on which the resistance of a conductor depends. Each one of them completed electric circuit with the help of a cell, an ammeter, a plug key and wire.

Shweta put nichrome wire of length '' in the circuit and after plugging the key, noted current in the ammeter.

Ayesha put nichrome wire of same thickness but twice the length i.e. '' in the circuit and after plugging the key, noted current in the ammeter.

Samridhi took copper wire of length '' and same thickness in the circuit and after plugging the key, noted current in the ammeter.

  1. (a)

    If the ammeter reading is X ampere with nichrome wire of length '', then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section ?

    1 mark
  2. (b)

    What happens to the ammeter reading if the area of cross-section of nichrome wire is doubled, keeping the length of wire '' the same ?

    1 mark
  3. (c)

    Define 'resistivity'. Write its SI unit. Compare the resistivity of an alloy with its constituents metals.

    2 marks

  4. OR

    (c) OR (i)

    Give reason: Tungsten is used almost exclusively for making the filament of electric lamps.

    2 marks

  5. OR

    (c) OR (ii)

    Give reason: Conductors of bread-toasters are made of an alloy rather than a pure metal.

    2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/5/1.

Hints

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

Hint 1

Recall and Ohm's law .

Hint 2

More resistance means less current for the same cell voltage.

Hint 3

For the OR part, think about what a filament or heating element must withstand.

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) ; doubling the length doubles resistance, so with the same cell is halved. Ammeter reading = A.

    1 mark

  2. (b) ; doubling the area halves the resistance, so current doubles. Ammeter reading = A.

    1 mark

  3. (c) Resistivity () of a material is the resistance of a conductor of that material having unit length and unit area of cross-section ().

    1 mark

  4. SI unit: ohm metre (m).

    ½ mark

  5. Resistivity of an alloy is generally higher than that of its constituent metals.

    ½ mark

  6. (c) OR (i) Tungsten has a very high melting point (about 3380 °C), so it can be heated till it glows (white hot) without melting.

    1 mark

  7. (c) OR (ii) An alloy has higher resistivity than pure metals, so it produces more heat, and it does not oxidise (burn) readily at high temperatures.

    1 mark

Answer: (a) X/2 A; (b) 2X A; (c) resistivity = resistance of unit length and unit cross-section area, unit Ω m, alloy has higher resistivity; OR (i) high melting point; (ii) high resistivity and no oxidation at high temperature

Where the marks are

  • Reading becomes X/2 (1 mark)
  • Reading becomes 2X (1 mark)
  • Correct definition of resistivity (1 mark)
  • SI unit Ω m (½ mark)
  • Alloy has higher resistivity than constituent metals (½ mark)
  • OR: Tungsten has high melting point (1 mark)
  • OR: Alloy has high resistivity / does not oxidise readily 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 paper2026 board paper, set 31/5/1: 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.