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(i) Draw the pattern of the… (Class 10 Science 2025, Q36A)

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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(A)

Set in the CBSE Class 10 board exam of 2025, paper 31/4/1, 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 answerCompetency-basedMagnetic Effects of Electric Current

(i) Draw the pattern of the magnetic field lines for the two parallel straight conductors carrying current of same magnitude 'I' in opposite directions as shown. Show the direction of magnetic field at a point O which is equidistant from the two conductors. (Consider that the conductors are inserted normal to the plane of a rectangular cardboard.)

(ii) In our houses we receive A.C. electric power of 220 V. In electric iron or electric heater cables having three wires with insulation of three different colours – red, black and green are used to draw current from the mains.

(a) What are these three different wires called? Name them colourwise.

(b) What is the potential difference between the red wire and the black wire?

(c) What is the role of the wire with green insulation in case of accidental leakage of electric current to the metallic body of an electrical appliance?

Figure in the paper: Two long straight vertical conductors drawn normal to a rectangular cardboard. The left conductor is marked I with a downward arrow (current into the page); the right conductor is marked I with an upward arrow (current out of the page). A point O is marked midway between them. 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

Use the right-hand thumb rule separately for each wire: the thumb points along the current and the curled fingers give the field.

Hint 2

Work out the direction of each wire's field at O, then decide whether the two add or cancel.

Hint 3

For (ii), recall the standard colour code of household wiring and why metal-bodied appliances are earthed.

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) Pattern: Around each conductor the field lines are concentric circles lying in the plane of the cardboard. They are closer together near each wire and spread out farther away. Between the two wires the lines crowd together.

    1 mark

  2. (i) Directions (right-hand thumb rule): The left conductor carries current into the cardboard (⊗), so its circles run clockwise. The right conductor carries current out of the cardboard (⊙), so its circles run anticlockwise. At the midpoint O, both fields point the same way: perpendicular to the line joining the conductors, towards the bottom of the figure. The two fields therefore add, and the resultant field at O is strong and points downward in the plane of the cardboard. Show this with an arrow at O.

    1 mark

  3. (ii)(a) Red insulation – live wire. Black insulation – neutral wire. Green insulation – earth wire.

    1½ marks

  4. (ii)(b) The potential difference between the live (red) and neutral (black) wires is 220 V.

    ½ mark

  5. (ii)(c) The earth wire is a safety measure. It connects the metallic body of the appliance to a metal plate buried deep in the earth. If current leaks to the body, the body stays at earth's potential (zero) and the leaked current flows to the earth. So the user does not get a severe electric shock.

    1 mark

Answer: (i) Concentric circles: clockwise around the left (inward) wire, anticlockwise around the right (outward) wire; the fields add at O, pointing perpendicular to the line joining the wires. (ii)(a) Red – live, black – neutral, green – earth; (b) 220 V; (c) Earth wire keeps the metal body at zero potential and drains leaked current, preventing a severe shock.

Where the marks are

  • Correct pattern of concentric field lines around both conductors (1 mark)
  • Correct directions of the lines and of the field at O (1 mark)
  • Names live, neutral and earth wires colourwise (½ × 3 = 1½ marks)
  • Potential difference 220 V (½ mark)
  • Role of the earth wire as a safety measure keeping the body at earth potential (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.