Class 9 Physics | Punjab Curriculum and Textbook Board Syllabus 2025
Magnetism is a force that acts at a distance upon magnetic materials. These materials are attracted to magnets and are called magnetic materials.
Materials such as iron, nickel, and cobalt are magnetic materials because they are attracted to magnets.
Non-magnetic materials include brass, copper, wood, glass, and plastic as they are not attracted to magnets.
A magnet is an object that produces a magnetic field, which exerts a force on magnetic materials. A key property of a magnet is that it has north and south poles.
Magnetic materials, such as iron, nickel, and cobalt, are attracted by magnets. These materials do not generate a magnetic field of their own but are drawn to the magnetic force when a magnet is nearby.
The magnets exhibit the following properties:
If a bar magnet is suspended horizontally through a string and allowed to come to rest, it will point in north-south direction. The end of the magnet that points north is called the north magnetic pole (N), and the end that points south is the south magnetic pole (S).
Like poles repel and unlike poles attract.
Temporary magnets are the magnets that work only in the presence of a magnetic field of permanent magnets. Once the magnetic field vanishes, they lose their magnetic properties.
Permanent magnets are those which retain their magnetic properties forever.
Magnetic material such as iron or steel can be made a magnet. This is known as magnetization.
A magnetic field is the region around a magnet where another magnetic object experiences a force on it.
The pattern of a magnetic field around a bar magnet can be seen very easily by a simple experiment. If iron filings are sprinkled on a thin glass plate placed over a bar magnet, the filings become tiny magnets through magnetic induction. Now if the glass surface is gently tapped, the filings form a pattern. This pattern is known as the magnetic field pattern. This pattern can be better shown by lines that correspond to the path of the filings. These lines are called magnetic lines of force.
The strength of the magnetic field is proportional to the number of magnetic lines of force passing through unit area placed perpendicular to the lines.
Electromagnets are a kind of temporary magnets. An iron nail or rod becomes a magnet when an electric current passes through a coil of wire wound around it. This setup is called an electromagnet.
A magnetic relay is a type of switch that operates using an electromagnet. It is used as an input circuit that works with a low current for safety purposes.
A circuit breaker is a safety device designed to allow only a certain maximum current to pass through it. If the current becomes excessive, it automatically switches OFF the circuit, thereby protecting electric appliances from damage or burning.
It is observed that the magnetic field of a bar magnet is similar to that of a solenoid carrying current. This suggests that magnetism is caused by moving charges. In a solenoid, charges move through the wire, while in a bar magnet, magnetism is due to spinning and revolving electrons within atoms.
If the orbital and spin axes of the electrons in an atom are so oriented that their fields support one another and the atom behaves like a tiny magnet, the materials with such atoms are called paramagnetic materials, such as aluminium and lithium.
Magnetic fields produced by both orbital and spin motions of the electrons in an atom may add up to zero. In this case, the atom has no resultant field. The materials with such atoms are called diamagnetic materials. Some of their examples are copper, bismuth, water, etc.
There are some solid substances such as iron, steel, nickel, cobalt, etc. in which cancellation of any type does not occur for large groups of neighbouring atoms of the order of 10^16 because they have electron spins that are naturally aligned parallel to each other. These are known as ferromagnetic materials.
The group of atoms in this type of material form a region of about 0.1 mm size that is highly magnetized. This region is called a magnetic domain. Each domain behaves as a small magnet with its own north and south poles.
Grip the solenoid with the right hand such that the fingers are curled along the direction of current (from the positive to the negative terminal of the battery) in the solenoid, then the thumb points to the N-pole of the bar end. OR Grip the solenoid with the right hand so fingers curl in the direction of current, and the thumb points to the N-pole.
Soft iron has high magnetic permeability. Permeability is the ability of a material to allow magnetic flux or lines of force to pass through it when placed inside a magnetic field.
A magnetic field is the region around a magnet where another magnetic object experiences a force on it.
A fringe field is the curved part of the magnetic field that comes out from the gap between the poles of a magnet. It helps to magnetize the tape by entering the magnetic coating during recording.