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Answer the following. (Science 2026 31/1/1 Q39b)

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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(b)

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

Q39(b) · 5 marks · Long answerElectricity

Answer the following.

  1. (i)

    How many bulbs of resistance 8 each should be connected in parallel combination to draw a current of 2 A from a battery of 4 V?

    0 marks
  2. (ii)

    Name the device used for measuring electric current. How is it connected in a circuit?

    0 marks
  3. (iii)

    State Joule's law of heating.

    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

First find the total resistance the circuit must have to draw 2 A from 4 V.

Hint 2

For n equal resistors R₀ in parallel, the equivalent resistance is R₀/n.

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) Required total resistance: .

    ½ mark

  2. (i) .

    ½ mark

  3. (i) Let bulbs of be joined in parallel. Then ( terms) .

    ½ mark

  4. (i) , so . 4 bulbs should be connected in parallel.

    ½ mark

  5. (ii) The device used for measuring electric current is an ammeter.

    1 mark

  6. (ii) It is always connected in series in the circuit.

    1 mark

  7. (iii) Joule's law of heating: the heat produced in a resistor is directly proportional to the square of the current, to the resistance, and to the time for which the current flows. So .

    1 mark

Answer: (i) 4 bulbs; (ii) ammeter, connected in series; (iii) H = I²Rt (heat ∝ I², R and t)

Where the marks are

  • (i) Uses (½ mark)
  • (i) Gets (½ mark)
  • (i) Parallel relation (½ mark)
  • (i) bulbs (½ mark)
  • (ii) Ammeter (1 mark)
  • (ii) Connected in series (1 mark)
  • (iii) Correct statement of Joule's law / (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 31/1/1: 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.