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What are magnetic field… (Class 10 Science 2025, Q36a)

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ScienceCBSE Class 10 · Board exam 2025, set 31/6/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 36(a)

Set in the CBSE Class 10 board exam of 2025, paper 31/6/1, section D, question 36(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q36(a) · 5 marks · Long answerMagnetic Effects of Electric Current

What are magnetic field lines ? How is the direction of magnetic field at a point determined ? Draw the pattern of magnetic field lines of the magnetic field produced by a current carrying circular loop. Mark on it the direction of (i) current and (ii) magnetic field lines. Name the two factors on which the magnitude of the magnetic field due to a current carrying coil depends.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/6/1.

Hints

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

Hint 1

Think of what a compass needle does when placed near a magnet.

Hint 2

Near each point where the loop cuts the sheet, the loop behaves like a straight wire. What shape are the field lines around a straight wire?

Hint 3

Apply the right-hand thumb rule at each side of the loop. Then ask what happens to the field when you add more turns or increase the current.

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. Magnetic field lines are imaginary closed curves drawn around a magnet (or a current-carrying conductor). The tangent at any point on a field line gives the direction of the magnetic field at that point.

    ½ mark

  2. Direction of field at a point: place a small magnetic compass needle at that point. The north pole of the needle points along the direction of the magnetic field there.

    ½ mark

  3. Figure (described in words): Draw a circular loop held vertically and cut by a horizontal cardboard sheet at two points, P and Q. Mark the current with arrows, going up through the sheet at P and down at Q.

    Around P, draw small concentric circles with anticlockwise arrows (seen from above). Around Q, draw concentric circles with clockwise arrows. Moving away from the wire, the circles grow larger and less curved.

    At the centre of the loop, the lines become almost straight and parallel, all pointing the same way through the loop.

    Label (i) the direction of current on the loop with arrows, as given by the right-hand thumb rule.

    1 mark

  4. Label (ii) the direction of the magnetic field lines with arrows on the circles and on the straight lines at the centre, consistent with the current direction.

    1 mark

  5. Factor 1: the magnitude of the field is directly proportional to the current flowing through the coil.

    1 mark

  6. Factor 2: it is directly proportional to the number of turns of the coil, because the fields of the turns add up. (It also depends on the radius of the coil: field .)

    1 mark

Answer: Field lines are imaginary curves whose tangent gives the field direction; direction is found with a compass needle (N-pole points along the field). The figure shows concentric circles near the wire and straight parallel lines at the centre, with current and field directions marked. Field depends on the current and the number of turns (also the radius).

Where the marks are

  • Defines magnetic field lines (½ mark)
  • States that a compass needle's north pole gives the field direction (½ mark)
  • Correct field pattern with the direction of current marked (1 mark)
  • Direction of magnetic field lines marked correctly (1 mark)
  • Any two factors: current, number of turns, radius of coil (1 + 1 marks)

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 paper2025 board paper, set 31/6/1: 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.