Introduction to Magnetism

Magnetism

• Magnetism is a force that attracts or repels certain materials
• Lodestone is a naturally occurring ore of iron oxide (Fe3O4) that possesses magnetic properties
• Early civilizations used lodestone for navigation
• Magnets have north and south poles that attract or repel each other
• Artificial magnets are made from iron materials in various shapes (bar magnets, horseshoe, needles etc)
• A freely suspended magnet aligns itself along the Earth's north-south direction
• Induced magnetism is a temporary magnetism in a material when placed near a magnet, which disappears when the magnet is removed
• Magnetic materials induce opposite polarity from applied magnet, and similar polarity from more distant pole
• Magnetic induction is the process of inducing a magnetic field in a material by an external magnetic field
• Magnetic materials are attracted to magnets due to induction preceding attraction
• Magnetic fields are represented by lines, with stronger fields having more closely spaced lines outside the magnet, directing from the north to south pole
• Magnetic Field Lines: Continuous closed curves
• Tangent to a field line indicates magnetic field direction
• Lines do not intersect
• Earth's magnetic field is responsible for a compass needle aligning north-south
• Earth's magnetic field is similar to a bar magnet, with the magnetic north pole near the geographic South pole.
• Neutral points are places where the Earth's horizontal magnetic field cancels out the magnetic field of a nearby magnet resulting in a zero field.
• Magnetic fields are stronger near the poles of a magnet and weaker further away
• Magnetic field lines are not always straight, they can curve.
• The Earth's magnetic field is not uniform in all locations.

Electromagnets

• Electromagnet is a temporary magnet using a coil of wire around a magnetic material
• Strength of electromagnet is dependent on current and turns of wire
• Electromagnet's strength can be changed by increasing or decreasing the current through the wire or increasing the number of turns
• Electromagnet loses its magnetism when the current is switched off
• Used in many applications: lifting heavy iron objects, electric bells, relays, electric motors and generators
• Electromagnets are made of soft iron, which has low retentivity
• Electromagnets can be in different shapes (I-shaped or U-shaped)

Explore magnetism, a fundamental force attracting or repelling materials. Learn about lodestones, the magnetic properties, the poles of magnets, and induced magnetism. Understand how magnetic fields interact and align with Earth's magnetic field.