Understanding the Dynamo The dynamo, which is a power generator, can be simple or complex. The simplest type of dynamo is a battery. A battery produces current that flows in only one direction and aligns the compass needle with the magnetic axes. The alternator is a more complex form of a dynamo. It generates alternating current that flows in both directions. Alternating current does not align the compass needle because the current flow changes direction about sixty times a second. The compass needle simply does not have time to move every time the current changes direction. When conducting experiments to investigate the magnetic field, it is better to use a battery or a direct current generator (dynamo system) because of the need for a steady flow of current in one direction.  Dynamo Systems Each planet in our solar system is part of a larger dynamo system. Five of the dynamo systems are fully developed and produce large magnetic fields, which protect the planets’ atmosphere. These planets are Earth, Jupiter, Saturn, Uranus and Neptune.The current flow around a planet is contained within a narrow passage called ring current, which is generally inline with the plane of the sun and the magnetic equator. Current Flow and Field Strength  The Straight Wire When current is flowing through a straight wire, the magnetic lines of force will be in the shape of circles surrounding the wire when looking at the wire from the end. The lines of force will be the strongest close to the wire. The lines of force will be weaker furthest from the wire.The Direction of Current Flow Guides the Compass Needle When a compass needle is positioned next to a current-carrying conductor, the needle will line up perpendicular to the wire. If the current is moving from west to east, the compass needle will point north and south. If the current is flowing from north to south, the compass needle will turn 180 degrees and point east and west. This means that the direction of the current flow will determine which way the compass needle points. The Moving Poles Earth’s magnetic North Pole moves 100 meters each day. It will not be in the same place it was yesterday, and it will be found somewhere else tomorrow. Some scientists are still trying to figure out what causes the movement, as they ask the following questions: “Is the magnetic axis moving relatively to the planet, or is the planet moving relatively to the magnetic axis?” We now know that the planet is moving because the magnetic axis is relatively fixed. The Moving Planet The compass needle always points to the magnetic North Pole but it does not always point to the same location on the ground. Since the magnetic axis is fixed relatively to the magnetic equator, the entire magnetic field would have to move each day along with the magnetic North Pole. Since we know that the magnetic axis stays aligned with equator, the magnetic axis does not move away from the planet, but the planet moves away from the magnetic axis. This means that each day the planet moves away from the magnetic axis by 100 meters. The North and South poles are not moving beneath the surface of the planet. The planet is constantly moving away from and around the magnetic axis. The movement of the poles was once attributed to the shifting of a dynamo beneath the surface of the planet. Now it is understood that there is no dynamo within the planet and that the planet moves around the magnetic axis. The magnetic axis is stationary except for rotation, while the planet wobbles when it moves around like a ball placed unevenly on a shaft. The Dynamo System The magnetic field, radiation belts, and planet are all components of the dynamo system. The radiation belts cannot exist without the planet. The magnetic field cannot exist without the radiation belts. The radiation belts cannot exist without the magnetic field. They were formed as a single unit and will die together as a single unit.  Solar Wind and Ring Current The dynamo system does not fuel itself. It is fueled by charged particles from the sun. The solar wind brings in the charged particles. The magnetic field’s lines of force capture the charged particles and funnel them into the dynamo system. The particles are moved down the lines of force toward the North and South Poles. The movement of the charged particle down the lines of force is part of the process that produces the electric current, which is called ring current. Ring current gets its name because the current flows in a ring pattern as it moves around the planet. Also, the radiation belts are in the shape of ovals or rings. On Earth, the compass needle always lines up perpendicular to the flow of ring current and parallel to the magnetic axis. The Magnetic Field’s Fuel The magnetic field has the intensity it does because the dynamo system is able to trap large amounts of charged particles, from the sun and other areas in space. It uses the particles as fuel when they flow through the dynamo system. As new particles come into the system, the used ones are expelled.  Ring Current Ring current is like a vast invisible river where currents flow without resistance. Positively charged particles flow westward and negatively charged particles flow eastward like cars in opposite lanes of a freeway. It is a very dynamic process. The flow of particles is so thick that they appear to occupy the same space. Other particles from the magneto tail ride the field’s lines down to the polar-regions and create the beautiful aurora in Earth’s atmosphere. Ring current extends from about 8,000 kilometers to nearly 30,000 kilometers from the surface and occupies nearly the same zone as the much more energetic Van Allen belts. Ring current particles carry energy. It is not a complete equatorial ring like Saturn’s rings and its strength increases and decreases with the activity in the magneto tail region. It is always at its strongest on the night-side of the Earth. The Unsteady Flow We know that the current flowing in the dynamo system will affect the compass needle in the same way that the current flowing from a battery will affect the compass needle. However, there is a big difference between the current flow in a battery and that in the radiation belts. The current flow from a battery has a constant strength. That found in the radiation belts is not constant. The strength of the current in the radiation belts changes because of the different quantities of charged particles coming from the sun. Some of the charged particles that make up the radiation belts come from outside the solar system and are known as cosmic rays. A Protective Barrier The magnetic field extends out into space and helps protect the earth from radiation by forming a protective barrier called a bow shock. The barrier deflects the charged particles toward the North and South Poles and protects the planet from direct bombardment.  Our Solar System, Chapter 2 Magnetosphere, Chapter 3 Radiation Belts, Chapter 4 Magnetic Fields, Chapter 5 Earth’s Dynamo, Chapter 6 Dynamo Systems, Chapter 7 The Sun as a Dynamo, Chapter 8 Auroras Chapter 9 Space Weather Chapter 10 References |