Magnetism

Iron Filings and Pole Identification
- When a magnet is immersed in iron filings, the filings adhere to the ends of the magnet.
- This phenomenon illustrates that the attraction is strongest at the extremities of the magnet, known as the poles.
Magnetic Orientation
- A freely hanging magnet consistently aligns itself along the north-south axis.
- The end directed towards the geographic north is termed the north pole (N), while the end pointing towards geographic south is known as the south pole (S).
Existence of Magnetic Poles
- Magnetic poles are always found in pairs; isolated magnetic poles do not occur in nature.
Attraction and Repulsion of Poles
- Like poles repel each other, while opposite poles attract:
- When a north pole approaches another north pole, repulsion is observed.
- Conversely, a north pole near a south pole will lead to an attractive force between the two.

Ferromagnetic Materials
- Examples include iron, cobalt, and nickel.
- These materials are attracted to magnets and have internal structure characterized by domains that align orderly under a magnetic field, consisting of tiny magnets each possessing its own north and south pole.
- Ferromagnetic materials include strong magnetic alloys.
Non-Magnetic Materials
- Examples include copper, glass, brass, and wood.
- Such materials do not experience attraction to magnets; their internal domains are randomly aligned, negating the magnetic effect.

Definition
- Magnetic field lines are conceptual curves that illustrate the magnetic field's shape and direction. They emanate from the north pole and terminate at the south pole, forming continuous closed loops.
- Important characteristics of magnetic field lines include:
- They never intersect.
- The density of the lines indicates the strength of the magnetic field (higher density correlates to stronger fields).
- The direction of the lines (indicated by tangents) symbolizes the vector nature of the magnetic force.

The proximity or density of the field lines correlates positively with the strength of the magnetic field.
Field lines originate from the north pole and converge at the south pole.
Field lines do not cross one another.
Each point within the magnetic field has both direction and magnitude represented as a vector.
The magnetic field is stronger at the poles due to denser field lines in those regions.

Stroking Method
- Involves rubbing a magnet along a piece of iron or steel in one consistent direction, which aligns the internal, random domains.
Electrical Method (Solenoid)
- This method includes enclosing a material within a coil (solenoid) and passing a strong direct current (DC) through it, generating a significant magnetic field that aligns the domains.
Induction
- Involves placing ferromagnetic material close to a strong, permanent magnet, which can cause temporary or permanent magnetization.
Industrial Magnetizer
- Employs high-current, short-duration pulses to create extensive magnetic fields for rapid and precise magnetization, often enabling multi-pole magnetization.

Heating (Curie Temperature)
- When a magnet is heated beyond its specific Curie temperature, it undergoes thermal agitation. For iron, this temperature is 770°C, while for nickel it is 358°C, which disrupts the alignment of magnetic domains permanently.
Alternating Current (AC) Field
- Involves placing a magnet inside a solenoid, applying a strong AC current that is gradually reduced to zero, allowing the domains to randomize.
Physical Impact (Shocking)
- Repetitive hammering, dropping, or vibrating of the magnet results in structural disturbances that misalign magnetic domains.
Reverse Magnetic Field
- Exposure of the magnet to a strong magnetic field in the opposite direction can negate its magnetic properties, effectively demagnetizing it.

Induced magnetism refers to the phenomenon whereby a magnetic material becomes temporarily magnetized upon being placed within the magnetic field of another magnet, without physical contact or permanent alteration.

While in the presence of a magnetic field, the material's tiny magnetic domains rearrange.
As a consequence of this rearrangement:
- One end of the object becomes a temporary north pole.
- The other end becomes a temporary south pole.
On the removal of the influencing magnet, the material typically returns to a non-magnetized state (especially observable in materials like soft iron).

Feature	Soft Iron	Steel
Ease of Magnetization	Gets magnetized very easily	Harder to magnetize
Retention of Magnetism	Loses magnetism quickly	Retains magnetism for a long time
Nature of Magnet	Temporary magnet	Permanent magnet
Magnetic Strength Control	Changes quickly with an applied field	More stable once magnetized
Common Use	Electromagnets, transformers	Permanent magnets, tools

Feature	Electromagnet	Permanent Magnet
Need for Electricity	Not required	Required to work
Control of Magnetism	Cannot be turned off easily	Can be switched on/off
Strength Control	Fixed strength	Strength can be adjusted
Core Material	Usually steel or hard magnetic material	Soft iron core with coil
Uses	Compasses, refrigerator magnets	Electric bells, cranes, motors

Permanent Magnet: An example includes a traditional fridge magnet, which remains magnetic continuously.
Electromagnet: An example is an electromagnet used in a crane which only exhibits magnetic properties when current is supplied to the coil.

A permanent magnet consistently retains its magnetic properties, whereas an electromagnet only operates when an electric current is supplied and can be regulated according to need.