1. Magnets and Magnetic Fields
Magnetism
Magnets and Magnetic Fields

2. Magnets
Magnets – objects, usually metallic, that can attract or repel certain other objects, such as iron
Have two poles: North and South (or North-seeking and South-seeking)
Will point toward the Earth’s magnetic poles
North points toward Earth’s Magnetic South Pole and South points Earth’s Magnetic North Pole
Like poles repel and opposite poles attract
No matter how many times you cut a magnet, it will always have both a North and South pole
Used in multiple applications – electromagnets, motors, recording devices, maglev trains
Earth acts like a giant magnet

3. Magnetic Domains Moving charges cause magnetic fields
Every electron or proton is constantly in motion
Always generating a magnetic field
Most charged particles cancel each other out
Some substances have the charges moving in such a way that the magnetic fields line up
Ferromagnetic – includes iron, cobalt, and nickel
Can be effected by a magnet
In ferromagnetic materials, the charges group together in large groups called magnetic domains
Most of the time, the domains are oriented randomly – nonmagnetic
In natural magnets or in substances effected by a magnet, the domains are oriented more closely
Aligned magnetic domains enhance the magnetic field

4. Magnetic Domains

5. Magnetic Domains Substances can be made into permanent magnets
Prolonged exposure to a permanent magnet can cause ferromagnetic materials to become magnetic
Stroking iron with a magnet
Being near a magnet for a long enough time – induced magnetism
Magnetically soft materials are easy to magnetize, but lose their magnetism easily
Magnetically hard materials do not magnetize easily, but will keep their magnetism longer
To break a magnet, expose it to heat and cold or hammer it

6. Magnetic Fields
Magnetic field – a region in which a magnetic force can be detected
Surrounds any magnetized material, including Earth
Earth’s magnetic field shields us from ultraviolet radiation, x-rays, gamma rays, and the solar wind from space and traps the atmosphere close to the surface
Magnetic fields run from the North Pole to the South Pole of a magnet
Can be drawn similar to electric field lines
The more lines, the stronger the field
Magnets are stronger at the poles

7. Magnetic Fields
Magnetic Flux – the number of magnetic field lines that cross a certain area at right angles to that area
Symbol is ΦM
Magnetic flux = surface area * magnetic field component normal to the plane of surface
ΦM = A * B * cosθ
A = surface area (meters squared, M2)
B = Magnetic Field Strength (Teslas, T)
θ = angle between perpendicular and the magnetic field , usually going to be 0.0° at our level

8. Magnetic Field of a Bar Magnet
Section 1 Magnets and Magnetic Fields
Chapter 19
Magnetic Field of a Bar Magnet

9. Magnetic Fields
Earth’s magnetic field is currently oriented so that magnetic south is in the geographic north and magnetic north is located in geographic south
The magnetic field reverses itself periodically
Can be observed at sea-floor spreading areas
Magnetic declination – the difference between true north (as defined by the Earth’s axis of rotation) and the North Pole of a compass
Varies everywhere on Earth
Essentially zero in the center of North America
20° East of true North in the State of Washington
Source of Earth’s magnetic field is believed to be convection currents in the molten core of the Earth
As the molten metal moves, it induces a magnetic field
Stronger planetary magnetic fields may cause a faster planetary rotation

10. Earth’s Magnetic Field
Section 1 Magnets and Magnetic Fields
Chapter 19
Earth’s Magnetic Field