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NCERT Magnetic effects of electric current class 10 science chapter note

1. What is a magnet?

Answer : Magnet is a substance which attracts magnetic material and it points in north and south direction, when suspended freely.

Loadstone – Fe₃O_4M

Magnet effect of electric current:

Whenever a current is passed through a conductor a magnetic field is created around it. It is known as magnetic effect of electric current.

Different Magnets:

1. Bar Magnet
2. Horse shoe magnet

Properties of Bar magnet:

Attractive property:

Like poles repel each other and unlike poles attract each other.

Directive Property:

If you suspend a bar magnet freely, always points north and south direction.

Magnetic poles always exist in pair. If we devide the magnet, then we will get 2 poles.

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Magnetic Field:

The reason around which magnetic field force is detected is known as magnetic field. It is a vector quantity.

Magnetic field line:

The imaginary path along with a unit north pole would move if it is free to do so.

• They are closed continuous curves.


• Magnetic field lines start from north pole and end at south pole outside the magnet.


• Inside the magnet the direction of magnetic field is from south pole to north pole. So it is called closed continuous curves.


• The direction of magnetic field at a point is represented by a tangent drawn at that point.


• The direction of magnetic field at any point is along the direction of north pole of magnetic needle placed at that point.


• No 2 magnetic lines can intersect each other. If 2 magnetic field lines intersect each other at one point then there can be two tangents. At this point a magnetic needle has to show two directions which is not possible. Hence no 2 magnetic field lines intersect.


• The relative strength of magnetic field is determined by degree of closeness of magnetic field lines.


• Near the poles magnetic field lines are closed to each other, Hence the magnetic field is strong near the pole.


• If the magnetic field lines are wide apart in any region , then field is weak at that point.

Uniform magnetic field

The magnetic field is said to be uniform if the magnitude and direction is same at each point of the region.

The current flows through a conductor and a compass is placed near it, then the compass will be deflected. the deflection of compass is determined by snow rule.

Snow Rule:

When current flows in a conductor from south to north direction over which a compass is placed . then the north pole of the needle will be deflected towards pole.

Ampere swimming rule

Imagine a man swims always facing towards the conductor such that the current will enter its feat and leaves at his head, then north pole of magnetic needle will be deflected along his left hand.

Magnetic field due to a current carrying straight conductor:

When current flows through a straight conductor a magnetic field is created around it. The pattern of magnetic field lines is in form of concentric circle and centre lies on one point of conductor.

Imagine you are holding a conductor in right hand such that the thumb will flow point the direction of flow of current. The curl of the finger will represent the direction of magnetic field.

Factors on which the strength of the magnetic field at a point around a straight current carrying conductor depends:

The strength of the magnetic field at any point around the straight current carrying conductor.

1. Is directly proportional to the amount of current flowing through the conductor. B ∝ I
2. Is inversely proportional to the distance of the point from the straight conductor.

Magnetic field due to current carrying circular loop:

The magnetic field line at the centre of circular loop will appear as a straight line. The strength of the magnetic field at the centre of current carrying circular loop is directly proportional to the amount of current flowing , no of turns and inversely proportional to radius of coil.

B ∝ I , B ∝ n, B ∝ 1/r

Magnetic field due to a solenoid

A solenoid is coil of insulated copper wire closely wound in the form of a cylinder.

A current carrying solenoid will behave as a bar magnet, the pole of the solenoid can be determined clock faced rule.

Inside the solenoid, the magnetic field lines are parallel to each other. It means that the magnitude and direction of magnetic field as same at every point inside the solenoid. This indicates that the magnetic field is uniform inside the solenoid.