Chapter 12 · Magnetic Effects of Electric Current

NCERT Class 10 Science Chapter 12 Intext Questions (Page 200)

All 3 questions of NCERT Class 10 Science Chapter 12 Intext Questions (Page 200) — Magnetic Effects of Electric Current — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   Draw magnetic field ​lines ​around ​a ​bar ​magnet.
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   Closed lines run from north to south outside the magnet and south to north inside, crowded near the poles, with arrowheads and no crossings.

   The field lines are closed curves. Outside the magnet they emerge from the north pole, curve round through the space on either side and enter the magnet at the south pole; inside the magnet each line continues from the south pole to the north pole, so it closes on itself. Every line carries an arrowhead showing this direction. The lines are crowded together near the two poles, where the field is strongest, and are widely spaced near the middle of the sides, where it is weakest, and no two of them ever cross. The figure shows the completed drawing.

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2. Q2
   List the ​properties ​of magnetic ​field ​lines.
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   Field lines show the field direction, run north to south outside a magnet, are closed curves, show strength by their closeness and never cross.

   The properties of magnetic field lines are: (i) A field line is the path along which a free north pole would tend to move, and the direction of the field at a point is the tangent to the line there — the direction the north pole of a compass needle placed there would take. (ii) Outside a magnet the lines run from the north pole to the south pole, and inside the magnet from the south pole to the north pole, so every field line is a closed continuous curve with no beginning and no end. (iii) The lines are crowded together where the field is strong and are spread apart where it is weak, so their relative closeness shows the relative strength of the field. (iv) No two field lines ever intersect, because at the crossing point the field would have two directions and a compass needle cannot point two ways at once.

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3. Q3
   Why ​don’t ​two magnetic field lines ​intersect ​each ​other?
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   At a crossing point the field would have two directions at once, which is impossible, so field lines never intersect.

   The tangent to a magnetic field line at any point gives the direction of the magnetic field at that point. If two field lines crossed at a point P, there would be two different tangents at P, so the magnetic field at P would have two different directions at the same time, and a compass needle placed at P would have to point in two directions at once. That is impossible, because the field at a point has one definite direction. Hence two magnetic field lines never intersect each other.

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