Magnetism (general)

Define magnetic field

A region surrounding a magnet in which a body of magnetic material experiences a magnetic force

• Direction  of a magnetic field line at a point = direction in which the N pole of a compass needle placed at the point would point

What is magnetic declination?

The angle between magnetic and geographic north (the norths do not coincide)

What is the theory of magnetism?

If a magnet is cut into smaller pieces, each piece becomes a magnet with a north and south pole

How does magnetization with stroking work?

• Magnetic domains in an unmagnetized bar point at random directions

• Magnetic domains point in the same direction when a bar magnet is brought near the bar, producing north and south poles

*Atomic magnets at the ends tend to fan out due to repulsion between like poles

How do we perform magnetization with the electrical method?

1. Place the steel or iron object in a coil of wire

2. Pass a direct current through the solenoid for a few seconds

3. A magnetic field is produced on the solenoid

What is the right hand grip rule?

• Fingers curl in the direction of current flow

• Thumb points in the direction of the north pole

What are the differences between iron and steel?

Iron

• Soft magnetic material

• Easy to magnetize and demagnetise

• Used to make temporary magnets

Steel

• Hard magnetic material

• Hard to magnetize and demagnetise

• Used to make permanent magnets

What is the goal of demagnetization?

Cause atoms in a magnetic domain to point in a random direction

How does demagnetization through heating work?

Atoms of the magnet vibrate vigorously and lose their alignment

How does demagnetization through hammering work?

Alters the alignment of magnetic domains

How does demagnetization through the electrical method work?

1. Place the magnet into a solenoid of alternating supply

2. As the current flows, slowly withdraw the magnet in the east west direction until it is far from the solenoid

Magnetic domains misalign until the magnet is slowly pulled out

What is the purpose of magnetic shielding?

Remove magnetic fields

How is magnetic shielding achieved?

Through surrounding the object with soft iron so the lines of magnetic force concentrate in the soft iron

What is the purpose of magnetic keepers?

To ensure that the magnetic domains remain aligned in the same direction

Why do magnets become weaker after time if not stored properly?

Free poles at the ends repel one another