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Answer the following. (Science 2026 31/2/1 Q39b)

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ScienceCBSE Class 10 · Board exam 2026, set 31/2/1 · 5 marks · Long answer

CBSE Class 10 Science 2026: question 39(b)

Set in the CBSE Class 10 board exam of 2026, paper 31/2/1, 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 answerMagnetic Effects of Electric Current

Answer the following.

  1. (i)

    Draw the pattern of magnetic field lines through and around a current-carrying circular loop.

    0 marks
  2. (ii)

    State the rule to find out the direction of the magnetic field inside and around the circular loop.

    0 marks
  3. (iii)

    Give reasons :
    (I) Why should a burnt-out fuse be replaced by another fuse of identical rating only, in an electric circuit ?
    (II) Why is soft iron-core used in making an electromagnet ?

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/2/1.

Hints

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

Hint 1

Each small part of the loop behaves like a straight wire producing circular field lines.

Hint 2

Use the right-hand thumb rule to decide the direction of the circles at each point.

Hint 3

For the fuse, think what happens if the rating is too high or too low; for soft iron, think about switching the magnet off.

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) Diagram (described): Draw a circular loop standing perpendicular to the plane of the paper, cutting it at two points P and Q. Around each of P and Q draw concentric circles, small near the wire and larger farther away. Near the centre of the loop the field lines become nearly straight and parallel, passing through the loop perpendicular to its plane.

    1 mark

  2. Mark directions: current coming out of the paper at P and going into the paper at Q; by the right-hand thumb rule the field lines are anticlockwise around P and clockwise around Q, so inside the loop all lines point in the same direction.

    1 mark

  3. (ii) Right-hand thumb rule: Imagine holding the current-carrying wire (each part of the loop) in the right hand with the thumb pointing along the current; the direction in which the fingers curl gives the direction of the magnetic field lines.

    1 mark

  4. (iii)(I) A fuse of higher rating would not melt when the current exceeds the safe limit, so it would not protect against overloading; one of lower rating would melt even at normal current and the appliance would not work. Hence a fuse of identical rating must be used.

    1 mark

  5. (iii)(II) Soft iron becomes strongly magnetised as soon as current flows through the solenoid and loses its magnetism immediately when the current is switched off, so the electromagnet can be turned on and off as needed.

    1 mark

Answer: (i) Concentric circles around each point where the loop cuts the paper, becoming straight and parallel at the centre; (ii) right-hand thumb rule; (iii)(I) higher rating fails to protect, lower rating melts in normal use; (II) soft iron magnetises and demagnetises quickly

Where the marks are

  • (i) Correct field pattern of a circular loop (1 mark)
  • (i) Correct directions of current and field lines (1 mark)
  • (ii) Statement of right-hand thumb rule (1 mark)
  • (iii)(I) Reason for same fuse rating (1 mark)
  • (iii)(II) Soft iron is easily magnetised and demagnetised (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Magnetic Effects of Electric Current, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/2/1: 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.