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(i) By using the given… (Class 10 Science 2025, Q36B)

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ScienceCBSE Class 10 · Board exam 2025, set 31/4/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 36(B)

Set in the CBSE Class 10 board exam of 2025, paper 31/4/1, section D, question 36(B), for 5 marks. Try it first; the hints and our step-by-step solution are below.

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

(i) By using the given experimental set-up, how can it be shown that :
(a) a force is exerted on the current-carrying conductor AB when it is placed in a magnetic field.
(b) the direction of force can be reversed in two ways.

(ii) When will the magnitude of the force be highest?

(iii) State Fleming's left hand rule.

Figure in the paper: Experimental set-up: a horseshoe magnet with poles N and S, a rod AB placed between the poles, connected through a rheostat/plug key K and a battery to a rail and a stand. Current direction marked through AB; the wire loop and stand are shown with a battery symbol and key K. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/4/1.

Hints

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

Hint 1

Think about what you would see happen to rod AB once key K is closed.

Hint 2

The force depends on two directions; changing either one changes the force.

Hint 3

For the rule, use three fingers of the left hand held at right angles: one each for field, current and force.

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)(a) Place rod AB between the poles of the horseshoe magnet and close key K so that current flows through AB. The rod is seen to be displaced (it moves). This shows that a force acts on the current-carrying conductor in the magnetic field.

    1 mark

  2. (i)(b) Way 1: Reverse the direction of the current in AB by reversing the battery connections. The rod is now displaced in the opposite direction.

    1 mark

  3. (i)(b) Way 2: Reverse the direction of the magnetic field by interchanging the poles of the magnet (S on top, N below). The rod again moves the opposite way.

    1 mark

  4. (ii) The force is highest when the direction of the current is at right angles (perpendicular) to the direction of the magnetic field.

    1 mark

  5. (iii) Fleming's left-hand rule: Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force (motion) on the conductor.

    1 mark

Answer: (i)(a) AB gets displaced when current flows; (b) reverse the current, or reverse the magnetic field. (ii) When the current is perpendicular to the magnetic field. (iii) Forefinger – field, middle finger – current, thumb – force, with all three mutually perpendicular on the left hand.

Where the marks are

  • Rod AB gets displaced on passing current, showing a force (1 mark)
  • Reversing the direction of current (1 mark)
  • Reversing the direction of the magnetic field (1 mark)
  • Force is maximum when current is perpendicular to the field (1 mark)
  • Correct statement of Fleming's left-hand rule (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 paper2025 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.