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Answer the following. (Science 2026 31/2/1 Q39a)

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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(a)

Set in the CBSE Class 10 board exam of 2026, paper 31/2/1, section C, question 39(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q39(a) · 5 marks · Long answerMagnetic Effects of Electric Current

Answer the following.

  1. (i)

    State the rule which gives the direction of force acting on a current-carrying conductor placed in a magnetic field.

    0 marks
  2. (ii)

    What is a fuse ? Why is it called a safety device ?

    0 marks
  3. (iii)

    Why are electrical appliances with metallic bodies connected to the mains through a three-pin plug, whereas an electric bulb is connected with a two-pin plug ?

    0 marks
  4. (iv)

    What will be the direction of force experienced by the conductor AB due to the magnetic field, when current flows in the direction shown ? Name the law you applied to find the direction.

    0 marks

Figure in the paper: Vertical conductor AB with A at top and B at bottom; electric current is shown flowing upward (from B to A). Four horizontal magnetic field lines with arrows pointing to the right cross the conductor. See it in the official paper.

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

For the force rule, use the left hand with three fingers mutually perpendicular.

Hint 2

Think what happens to a fuse wire when the current becomes too large.

Hint 3

For (iv), point the forefinger to the right (field) and the middle finger upward (current); see where your thumb points.

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) 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 along the magnetic field and the middle finger along the current, the thumb points in the direction of the force (motion) on the conductor.

    1 mark

  2. (ii) A fuse is a safety device, a short wire of low melting point connected in series with the circuit, which melts and breaks the circuit when excess current flows (overloading or short-circuit).

    ½ mark

  3. It is called a safety device because by breaking the circuit it stops the excess current and so prevents damage to the wiring and appliances and avoids fire.

    ½ mark

  4. (iii) A three-pin plug connects the metallic body of the appliance to the earth wire. The earth wire gives a low-resistance path for any leaked current to flow to the ground, so the body stays at earth potential and the user does not get an electric shock. A bulb has no metallic body that can be touched, so it needs no earthing and a two-pin plug is enough.

    1 mark

  5. (iv) Current in AB is upward (B to A) and the field is towards the right. Applying the rule with forefinger to the right and middle finger upward, the thumb points into the page. So the force on AB is perpendicular to the plane of the paper, directed into it.

    1 mark

  6. Law/rule applied: Fleming's left-hand rule.

    1 mark

Answer: (i) Fleming's left-hand rule; (ii) fuse – low-melting wire in series that melts on excess current, protecting circuit and appliances; (iii) three-pin plug earths the metallic body to prevent shock; bulb has no metallic body; (iv) into the page, by Fleming's left-hand rule

Where the marks are

  • (i) Correct statement of Fleming's left-hand rule (1 mark)
  • (ii) Definition of fuse (½ mark) and reason it is a safety device (½ mark)
  • (iii) Earthing of metallic body gives low-resistance path and prevents shock; bulb needs no earthing (1 mark)
  • (iv) Force into the page (1 mark)
  • (iv) Names 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 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.