Magnetic Fields

Magnetic Field of a bar magnet

I. Field of a bar magnet The forces of repulsion and attraction in bar magnets are due to the magnetic field that completely surrounds each magnet. Magnetic field lines extend outward from the north pole and flow back into the south pole.

I. Field of a bar magnet The field lines are more concentrated near the poles of the magnet so the magnetic field is said to be stronger near the poles.

Unlike poles (N-S) attract. Like magnetic poles (N-N or S-S) repel. I. Law of magnetic attraction

II.The Magnetosphere: –Magnetic Field of Earth Where is North? It depends! Do you mean Geographic North or Magnetic North? The Geographic (or True) North Pole is the point at 90 o N latitude which is aligned with the rotational axis of the Earth.

The Earth behaves as if there was a magnet in its interior. S N

II.The Magnetosphere: –Magnetic Field of Earth Where is North? The magnetic north pole is currently in northern Canada, but moves at an average rate of 15 km per year due to complex fluid motion in the liquid outer core of Earth. (more on this in a little while…)

The field lines of the Earth emerge from the South Magnetic Pole, curve around in space and converge again as they enter the Earth at the North Magnetic Pole. Similar to a bar magnet, Earth is surrounded by a 3- dimensional magnetic field called the magnetosphere. II. Declination vs inclination

A compass needle aligns itself along the direction of the magnetic field lines of the magnetosphere. Depending on your location, the difference between magnetic north and geographic north, called magnetic declination, can range from 0 o to 30 o. The magnetic declination for Martin High School (as of 2015) is 3° 50' E (and is moving about 7' farther eastward every year). [ 50' (50 minutes) is 50/60ths or 5/6ths of one degree. ] II. Declination vs inclination

Magnetic inclination, or dip angle, is the angle that the Earth’s magnetic field makes with the horizontal plane at a specified location. Magnetic inclination is 0° (horizontal) at the magnetic equator and 90° at both magnetic poles - straight up at the South Pole and straight down at the North Pole. The magnetic inclination for Martin High School (as of ) is 61° 24' downward.[ 24' (24 minutes) is 24/60ths or 4/10ths of one degree. II. Declination vs inclination

II.The Magnetosphere: –Magnetic Field of Earth The Earth is surrounded by a geomagnetic field with North and South Magnetic Poles. The Magnetic North Pole is the location to which the North end of a compass needle (or bar magnet) points.

II.Geomagnetic north vs. bar magnet north This means Earth’s magnetic North Pole is equivalent to the South Pole of a bar magnet!!

In other words, the North Pole of the Earth has a “South” polarity S N II.Geomagnetic north vs. bar magnet north

As a result, a the “N” tip of a compass needle will always point towards the North Pole. S N II.Geomagnetic north vs. bar magnet north

A compass is a magnetized piece of metal that can spin. S N N S The north tip of the compass (or the north pole of a magnet) always points towards the North Pole of the Earth North attracts South II.Geomagnetic north vs. bar magnet north

(The full name of a magnet’s north pole is “North-Seeking Pole”.) S N N S This means the North Pole of Earth is like the South Pole of a magnet!! North attracts South II.Geomagnetic north vs. bar magnet north

The Earth’s Magnetic Field is created in the same way you make an electromagnet. II.Geomagnetic north vs. bar magnet north

In an electromagnet the electrons move in a circling current around an iron nail. + - II.Geomagnetic north vs. bar magnet north

The Inner Core: Solid Iron and Nickel The Outer Core: Liquid Iron and Nickel The Mantle: A Dense and Mostly Solid Rock Material The Crust: A Thin Rock Material The Earth is made of four layers: II.Geomagnetic north vs. bar magnet north

The Outer Core of the Earth is an Electromagnet

The Inner Core is surrounded by the liquid Iron and Nickel of the Outer Core. As electrons flow in spinning currents through the core, the magnetic field is produced. The Earth’s rotation makes the electrons flow at very high speeds

A planet’s magnetic field is measured using an instrument called a Magnetometer.

Many spacecraft carry magnetometers to measure the Magnetic Field. Advanced Composition Explorer Mars Global Surveyor Galileo

The Geomagnetic Field (or Magnetosphere) also protects us from the Solar Wind:

Solar Wind Buffets Earth’s Magnetosphere

Coronal Mass Ejection

Intense Solar Wind resulting from a CME

Auroras Result from Solar Wind Interacting with Earth’s Magnetic Field

Earth’s Magnetic Field undergoes a Magnetic Reversal* every 200,000 years. *Yes - It flips 180 o !!

Planetary Magnetic Fields

Other Planets in our Solar System have Magnetic FieldsPlanet Magnetic Field Mercury 100 times weaker than Earth Venus 25,000 times weaker than Earth Earth 30,000 – 60,000 nT Mars 5000 times weaker than Earth

Other Planets in our Solar System have Magnetic Fields Planet Magnetic Field Jupiter 20,000 times greater than Earth Saturn 540 times greater than Earth Uranus 40 times greater than Earth Neptune ¼ that of Earth Pluto None that we know of

What causes a Planet’s Magnetic Field?

Mercury Mercury has a weak magnetic field – 100 times weaker than Earth This suggests Mercury has a liquid iron core in its interior.

Mercury The weak magnetic field could be also be partially due to Mercury’s slow rotation period. Mercury has a weak magnetic field:

venus Venus appears to lack the necessary ingredients to generate a magnetic field (no liquid core?) Venus has a very weak magnetic field. (About 25,000 times weaker than Earth’s) Venus also has very slow rotation.

mars Mars also has a very weak magnetic field. (About 5,000 times weaker than Earth’s) The core of Mars appears to have cooled so much that it is no longer liquid. The volcanoes in Mars are no longer active There is no earthquake activity on Mars

jupiter Jupiter has a strong magnetic field. (About 20,000 times stronger than Earth’s) The Terrestrial planets generate magnetic fields from iron at the center. But Jupiter has almost no iron core...

jupiter Jupiter has a strong magnetic field. The magnetic field of Jupiter is produced by the motion of liquefied metallic hydrogen found beneath the surface.

saturn Saturn also has a strong magnetic field. (About 540 times stronger than Earth’s) Saturn’s magnetic field is produced in the same way Jupiter’s is.

uranus The magnetic field in Uranus is about 40 times stronger than Earth’s It is probably created in the core of the planet, with ice, rather than with iron.

neptune The magnetic field in Uranus is about 1/4 times as strong as Earth’s It is probably created in the same way as Uranus

pluto We do not know if Pluto has a magnetic field. Because Pluto has a small size and a slow rotation rate (1 day in Pluto = 6.4 Earth days), it does not seem likely that Pluto has a magnetic field.

The end