# Induced magnetism and Neutral Points

## •    Magnetite (Fe3O4) is the naturally occurring ore of magnet. A magnet is a substance which attracts some specific materials. •    The materials which are attracted towards a magnet are called magnetic material and the materials which do not get attracted towards a magnet are called non-magnetic material. •    A bar magnet is the most common type of natural magnet available commercially. A magnet has some properties. North pole and South pole are the two poles of a magnet. A magnet can attract magnetic materials such as iron, cobalt, nickel, etc. Unlike poles of the magnets also attract each other whereas the like poles of the magnets always repel each other. A freely suspended magnet always point is north-south direction. •    A magnetic exerts attractive or repulsive force due to its magnetic field. Magnetic field is the space surrounding a magnet within which the magnet has its influence. The strength of magnetic field varies with distance i.e., the magnetic field at a point is inversely proportional to the square of distance from the magnet. •    A magnetic field around a magnet can be detected by using magnetic compass near it. A magnetic field can be traced in the form of magnetic field lines. Magnetic field lines are closed curves which start from North pole and end in the South pole outside the magnet, whereas they run from south to north within the magnet. No two lines of force will cut each other.•    A magnet can induce magnetism in other magnetic materials. Magnetic induction is the phenomenon of converting the magnetic materials into magnets by induced magnetism. •    Earth also acts as a large bar magnet due to the electric current in the liquid outer core.

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• Q1

State the procedure to draw a magnetic field line with the help of a magnetic compass?

Marks:5

A magnetic field line can be drawn by following the given procedure:

(i) Fix a sheet of white paper on a drawing board. Place the magnet on a sheet of white paper and mark the boundary of the magnet.

(ii) Take a small compass and a bar magnet. Now, place the compass near the north pole of the magnet. Then, mark the position of the two ends of the needle.

(iii) Move the needle to a new position such that the south pole of the magnet occupies the position previously occupied by its north pole.

(iv) Repeat the above steps till you reach the south pole of the magnet.

(v) Remove the compass and join the points marked on the paper by a smooth curve. This smooth curve represents a magnetic field line of the bar magnet.

(vi) The direction of the magnetic field is taken to be the direction in which the north pole of the compass needle moves.

• Q2

State the properties of magnetic lines of force.

Marks:3

Magnetic lines of force exhibit the following properties:

(i) Magnetic field lines are closed curves, starting from N- pole to S – pole outside the field.

(ii) Within the magnet, they run from S – pole to N – pole.

(iii) The lines of force have tendency to contract longitudinally near the poles.

(iv) The lines of force have tendency to exert lateral or sideway pressure i.e they repel each other laterally.

(v) No two magnetic field lines cut each other.

(vi) Number of lines coming out from the pole of the magnet depends on the nature of surrounding medium.

• Q3

Two magnetic lines of forces never intersect each other. Justify the statement.

Marks:2

The tangent to a magnetic line of force gives the direction of its magnetic field. If we are given a point where magnetic lines of force intersect each other then there will be two tangents showing two directions of magnetic field which is not practically possible. Thus, two magnetic field lines never intersect each other.

• Q4

Why a compass needle does not indicate exactly towards the actual north pole of the earth?

Marks:1

The geographic north pole of the earth and the earth’s magnetic South Pole do not coincide with each other. They are separated by a certain angle and therefore, a compass needle does not indicate exactly towards the actual north pole of the earth.

• Q5

Define magnetic field and also draw the pattern of magnetic field lines due to a bar magnet.

Marks:2

The region around the magnet where force of attraction or repulsion can be felt by magnetic materials is called magnetic field.