Class 12 Physics
Topic Tree of Magnetism and Matter
1. Bar Magnet and Gauss’s Law
- Bar magnet and Gauss’s law
- Properties of a bar magnet
- Terms related to bar magnet
- Magnetic field at a point on the axis of a bar magnet
- Magnetic field at a point on the equator of a bar magnet
- Force and torque on a bar magnet placed in a uniform magnetic field
- Potential energy of a magnetic dipole in a uniform magnetic field
- Solenoid is equivalent to a bar magnet
- Gauss’s law in magnetism
2. The Earth’s Magnetism
- The Earth’s magnetism
- Earth’s magnetic axis
- Angle of inclination
- Angle of dip
- Horizontal component of Earth’s magnetic field
- Neutral points
- Cause of Earth’s magnetic field
3. Magnetic Properties of Materials
(a) Diamagnetic substances
- Diamagnetic substances
- Cause of diamagnetism
- Properties of diamagnetic substances
(b) Paramagnetic substances
- Paramagnetic substances
- Cause of paramagnetism
- Properties of paramagnetic substances
- Curie’s law
(c) Ferromagnetic substances
- Ferromagnetic substances
- Cause of ferromagnetism
- Properties of ferromagnetic substances
- Temperature dependence of ferromagnetism
- Permanent magnets and electromagnets
Lecture Notes
Notes: Properties of Magnet
1. Basic Properties
- Attractive Property
- Magnet attracts small pieces of iron, cobalt, nickel, etc.
- Attraction is maximum at the ends of the bar magnet → called poles.
- Directive Property
- A freely suspended magnet always points towards the geographical north-south direction.
- End pointing north → north-seeking pole (north pole).
- End pointing south → south-seeking pole (south pole).
- Magnetic Poles Always Exist in Pairs
- Isolated poles do not exist.
- Even if a magnet is broken, each piece has both north and south poles.
- Law of Magnetism
- Unlike poles attract each other.
- Like poles repel each other.
2. Terms Related to Bar Magnet
- Magnetic Axis: Line joining the poles of the magnet.
- Magnetic Equator: Line passing through the centre of the magnet and perpendicular to the magnetic axis.
- Magnetic Dipole: Arrangement of two equal and opposite poles separated by a small distance.
3. Magnetic Dipole Moment of a Bar Magnet (m)
4. Magnetic Field Lines – Properties
- Closed curves starting from north pole (in air) and ending at south pole.
- Never cross each other.
- Always emerge/enter magnet surface normally.
- Density of field lines → proportional to magnetic field strength.
Activity
Fill in the Blank Questions – Properties of Magnet
- The attraction of a magnet is maximum at its _______.
- The ends of a magnet where attraction is maximum are called _______.
- A freely suspended bar magnet always points in the _______ direction.
- The end of a magnet pointing towards the geographical north is called the _______.
- The end of a magnet pointing towards the geographical south is called the _______.
- Magnetic poles always exist in _______.
- Unlike poles _______ each other, while like poles _______ each other.
- The line passing through the poles of a magnet is called the _______.
- The line passing through the centre of the magnet at right angles to the magnetic axis is called the _______.
- An arrangement of two equal and opposite poles separated by a small distance is called a _______.
- The magnetic dipole moment of a bar magnet is given by m=q_m×___
- The direction of magnetic dipole moment is from _______ pole to _______ pole.
- If a bar magnet is cut into two equal halves perpendicular to its axis, the dipole moment of each part becomes _______.
- If a bar magnet is cut into two equal halves along its axis, the dipole moment of each part remains _______.
- Magnetic field lines are _______ curves which start from the north pole and end at the south pole in air.
- Magnetic field lines never _______ each other.
- Magnetic field lines enter or leave the surface of a magnet _______.
- The strength of the magnetic field at a place is indicated by the _______ of field lines.
