A student fixes a sheet of white paper on a drawing board using some adhesive materials

A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.

a. Draw a diagram to show this pattern of iron filings.

b. Draw the magnetic field lines of a bar magnet showing the poles of the bar magnet as well as the direction of the magnetic field lines. 

c. i. How is the direction of magnetic field at a point determined using the field lines ? Why do two magnetic field lines not cross each other ? ORii. How are the magnetic field lines of a bar magnet drawn using a small compass needle ? Draw one magnetic field line each on both sides of the magnet.

Answer

a.

b.

c. i.

• By placing a compass needle on magnetic field lines, direction of north pole will give direction of magnetic field.
• If they cross or intersect , it means that at the point of intersection the compass needle would point into two directions, which is not possible. /
• If they cross or intersect, it means that at the point of intersection there will be direction of two resultant fields which is not possible.

c. ii.

• Take a small bar magnet, place it in the centre of the drawing sheet fixed on a drawing board and mark its boundary.
• Place a small compass needle near the north pole of the magnet, south pole of the compass needle points towards the north pole.
• Mark the position of two ends of the needle. Now move the needle to a new position such that the south pole of needle occupies the position previously occupied by the north pole and again mark the new position of the north pole. In this way proceed step by step till you reach the south pole of the magnet. Join the points marked to get a field line. Similarly draw one more field line on the other side of the magnet.