Introduction to Magnetic Fields

• Magnets are used in various applications, from refrigerator magnets to MRI machines.
• All magnets have north and south magnetic poles.
• Like magnetic poles repel each other, while unlike poles attract.
• Magnetic fields enable magnets to attract other magnetic materials.

Defining Magnetic Fields

• A magnetic field is an area around a magnet where its magnetism works.
• Magnets produce magnetic fields, interact with other magnets, and attract magnetic materials.
• An iron nail moves towards a bar magnet because of the magnetic field.
• The magnetic field's strength relies on distance from the magnet.
• Strength increases as distance decreases, and vice versa.

Detecting Magnetic Fields with a Compass

• Compasses determine direction using a magnetic needle that responds to magnetic fields.
• The north pole of a compass points to the south magnetic pole of an object because opposite poles attract.
• Earth is a giant magnet with two magnetic poles that are opposite to geographic poles.
• Earth's north geographic pole is near the south magnetic pole, and vice versa.
• A compass on a horizontal surface points north due to attraction to Earth's south magnetic pole (geographic north).
• Earth's magnetic poles undergo periodic reversals and variations.
• Magnetic poles are not perfectly aligned with the geographic north-south axis.
• The difference between magnetic and geographic north is called magnetic declination.
• Near a magnetic field, a compass needle aligns parallel to the field's direction.
• The compass needle's north pole points away from the magnet's north pole and towards its south pole.

Explaining Magnetic Field Lines

• Magnetic field lines visually represent the magnetic field around a magnet.
• Magnetic field lines show the magnetic field direction around a magnet.
• The direction of the magnetic field is always tangent to the magnetic field lines.
• Magnetic field lines do not cross each other.
• Magnetic field lines form closed loops from the north to the south magnetic pole.
• The spacing of field lines indicates field strength, lines are denser at the poles.

Ferromagnetic Materials

• Ferromagnetic materials like iron, nickel, and cobalt are easily attracted to magnets.
• These materials retain magnetic properties even after the magnetic field source is removed.
• Ferromagnetic materials are commonly used as materials for magnets.
• Unpaired electrons in the atoms cause ferromagnetic materials to exhibit higher magnetic susceptibility.
• Unpaired electrons cause a non-zero total magnetic field to be produced.
• Aligned magnetic fields of atoms form magnetic domains within the material.
• Magnetic domains are like miniature magnets.
• Without a magnetic field, magnetic domains are randomly arranged.
• Placing a magnet or electric current nearby makes the material a temporary magnet by aligning its domains.
• Magnetized ferromagnetic materials attract other magnetic materials.