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Answer the following. (Class 10 Science 2026, Q39B)

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

CBSE Class 10 Science 2026: question 39(B)

Set in the CBSE Class 10 board exam of 2026, paper 31/4/1, 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 answerCompetency-basedElectricity

Answer the following.

  1. (i)

    How much electric current will an electric iron draw from 220 V source if the resistance of its heating element when hot, is 55 ? Calculate the power consumed by the electric iron when it is operated at 220 V.

    0 marks
  2. (ii)

    In a house, 3 bulbs of 100 watt each, are lit for 5 hours daily and an electric heater of 1.0 kW is used for half an hour daily. Calculate the total energy consumed in a month of 30 days and its cost at the rate of ₹3.60 per kWh.

    0 marks
  3. (iii)

    With reason explain, why are alloys commonly used to make elements of electrical heating devices.

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/4/1.

Hints

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

Hint 1

Use Ohm's law for current, then P = VI.

Hint 2

Convert all energies to kWh before adding: 1 kWh = 1000 Wh.

Hint 3

Think about what property makes a material heat up a lot and survive high temperatures.

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)

    1 mark

  2. 1 mark

  3. (ii) Using :

    • Bulbs: per day
    • Heater: per day
    • Total per day
    1 mark

  4. Energy in 30 days units.
    Cost

    1 mark

  5. (iii) Alloys are used because their resistivity is higher than that of their constituent metals, so they produce more heat. They also do not oxidise (burn) readily at high temperatures.

    1 mark

Answer: (i) 4 A, 880 W; (ii) 60 kWh, ₹216; (iii) Alloys have high resistivity and do not oxidise readily at high temperature.

Where the marks are

  • I = 220/55 = 4 A (1 mark)
  • P = 220 × 4 = 880 W (1 mark)
  • Daily energy 1.5 + 0.5 = 2 kWh (1 mark)
  • Monthly 60 kWh and cost ₹216 (1 mark)
  • Alloys: higher 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 paper2026 board paper, set 31/4/1: 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.