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In our homes, we receive the… (Class 10 Science 2025, Q39)

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ScienceCBSE Class 10 · Board exam 2025, set 31/1/1 · 4 marks · Case-based

CBSE Class 10 Science 2025: question 39

Set in the CBSE Class 10 board exam of 2025, paper 31/1/1, section E, question 39, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q39 · 4 marks · Case-basedCompetency-basedElectricity

In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by underground cables. In our country the potential difference between the two wires (live wire and neutral wire) of this supply is 220 V.

  1. (a)

    Write the colours of the insulation covers of the line wires through which supply comes to our homes.

    1 mark
  2. (b)

    What should be the current rating of the electric circuit (220 V) so that an electric iron of 1 kW power rating can be operated?

    1 mark
  3. (c)(i)

    What is the function of the earth wire? State the advantage of the earth wire in domestic electric appliances such as electric iron.

    2 marks

  4. OR

    (c)(ii)

    List two precautions to be taken to avoid electrical accidents. State how these precautions prevent possible damage to the circuit/appliance.

    2 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

Convert 1 kW to watts and use the relation between power, voltage and current.

Hint 2

Pick a standard rating just above the current you calculate.

Hint 3

Think about what happens if the live wire touches the metal body of an iron.

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) Live wire: red insulation (brown in the newer convention).

    ½ mark

  2. Neutral wire: black insulation (light blue in the newer convention).

    ½ mark

  3. (b) W and V. Using : A.

    ½ mark

  4. The circuit must carry at least 4.54 A, so its current rating should be 5 A.

    ½ mark

  5. (c)(i) Function: the earth wire (green insulation) joins the metal body of the appliance to a metal plate buried deep in the earth. It gives any leakage current a low-resistance path to the ground, which keeps the body at the earth's potential.

    1 mark

  6. Advantage: if the live wire touches the metal body of the electric iron, the current flows to earth. The user does not get a severe electric shock.

    1 mark

  7. (c)(ii) Precaution 1 – Use a fuse (or MCB) of proper rating in the circuit.

    ½ mark

  8. Precaution 2 – Earth all metal-bodied appliances using the earth wire.

    ½ mark

  9. How the fuse helps: during overloading or a short circuit the fuse wire melts and breaks the circuit. This prevents damage to the circuit and appliances.

    ½ mark

  10. How earthing helps: leakage current flows safely to earth, preventing electric shock.

    ½ mark

Answer: (a) Live – red, Neutral – black; (b) I ≈ 4.54 A, so rating 5 A; (c)(i) earth wire gives low-resistance path for leakage current to earth and keeps body at earth potential, so user does not get a shock; (c)(ii) fuse (prevents damage from overloading/short circuit) and earthing (prevents shock from leakage current)

Where the marks are

  • Live wire red (½ mark)
  • Neutral wire black (½ mark)
  • Uses I = P/V to get ≈ 4.54 A (½ mark)
  • Concludes rating of 5 A (½ mark)
  • Earth wire provides low-resistance path to earth for leakage current (1 mark)
  • Advantage: prevents electric shock to user (1 mark)
  • Names fuse (½ mark) and earth wire (½ mark) as precautions
  • Fuse prevents damage due to overloading (½ mark)
  • Earthing prevents shock from leakage (½ 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.