Earth’s Magnetic Field 16.3

Compass – small bar magnet (needle) able to rotate and point North. Needle lines up with magnetic field. North pole of compass always points to south pole of permanent magnet. Loadstone – magnetic material discovered 500BC in Magnesia, Greeks used it to navigate. One end pointed North, the other end South.

Some animals can “sense” the earth’s magnetic field using small particles of iron oxide inside them.

Geographic N (“true north”) - where earths rotational axis intersects the surface Magnetic N – is really close to the geographic S pole Antarctica! Remember, the N needle of the compass always points toward the magnetic S

Declination – the earth’s geographic N and magnetic S are not at the exact place (degrees) Earth’s magnetic core- circulating dense molten material create electric currents which produce the magnetic field (i.e. Electromagnet)

Gauss – unit to measure magnetic field strength, earth’s field strength is only.5 gauss at the surface. A small permanent magnet has a field of 300-1,000 gauss at its surface. Magnetic pole reversal – happens about every 500,000 yrs; last one was 750,000 yrs ago, so we are overdue. we’re losing 7% field strength every 100 years, field should reverse in 2,000 years

Earth’s magnetic core (iron and nickel) highly conductive, so huge electric currents flow to produce Earth’s magnetic field. Other planets have magnetic fields so they also have moving molten cores, but our moon is too small and cold to have a molten liquid core.

The Sun has a magnetic field and rotates to make its “day” which is about 25 earth days at its equator and 35 days at the poles. This twists and distorts the surface/magnetic field and causes solar storms when the field lines snap back. This can disrupt magnetic devices on earth (cell phones and radio)

Energy to power the earth’s dense molten core comes from the interaction with the sun, the sun’s charged particles and its magnetic field

MRI – Magnetic Resonance Imaging, 1977 Main magnet- used to polarize nuclei of atoms in body Gradient magnet- turn on and off quickly to produce a cross sectional sliced image of a particular organ Nuclei in the body “resonate” (from applied radio waves) and absorb or release energy (at natural frequency) that is captured as an image based upon the density of tissue