Magnetism and Geomagnetism: Basics and Concepts

Transcription

1 Magnetism and Geomagnetism: Basics and Concepts Introduction: If you go by the term Geomagnetism, it consists of two segments. Geo means Earth and Magnetism means a property of a substance (for example a magnet made from soft raw iron) that can attract any substance closer (for example, opposite pole of another magnet) or repel any other substance away (for example similar pole of another magnet). Hence from the terminology it can be said in simple way that, Geomagnetism is the magnetic property of our earth. To understand the concept of Geomagnetism, we need to investigate the magnetism part first then it can be related with the Earth. 1

2 I think all of us are aware of bar magnet. It is consider being the most common type of magnets. One of the important characteristic of this magnet is presence of positive and negative pole on the opposite ends. At this point of discussion one fundamental question must be answered before moving ahead. The question is how magnets are made? Hmm. Let s look at the simplest way. Let s have a soft raw iron bar and a powerful magnet. Initially the raw iron bar you will consists of several very small iron atoms with existing positive and negative poles in unsystematic manner. Now, touch the strong bar magnet to one end of the raw iron, rub it through entire length and same process is applied for number of times and that s it! The raw iron would be converted into a magnet. And yes, I can hear what is there in your mind. When you rubbed the strong iron on the raw iron for number of time all the existing unorganized poles in the raw iron, it is systematically organized in a manner that two opposite ends of the iron bar is associated with opposite poles (in one end positive and on the other end negative pole). It is the crudest way of making magnet and followed in the past but for the understanding of the geomagnetism it is most fundamental. 2

3 In technical terms, Ferromagnetic materials like iron, nickel, cobalt etc. are associated with unpaired electron spins (as most of the atoms of the substances having electrons paired up in the orbitals with one spin up and one spin down resulted into cancelling each other s force which is not there in the ferromagnetic materials). In these kinds of materials, the net spin of the electrons is aligned in a direction and gave birth to two distinct poles viz. north and South Pole. As you have the basic idea of a bar magnet now let s talk about the magnetic field, an integral part of any magnet. 3

4 Magnetic Field: Magnetic field can be defined as the vector fields (having a definite direction and magnitude) formed by the magnet around it. Thus, magnets create their own magnetic fields resulted in to formation of magnetic field lines. The magnetic field directs from North Pole of the magnet to the South Pole while inside the magnet the field is from South Pole to the North Pole and hence it creates a closed loop. Let s have an experiment. Suppose we have a strong bar magnet. Now if we sprinkle some amount of iron filing on the bar magnet then you will observe that the iron filings are arranged in a manner. These arrangements of iron filing are nothing, but the magnetic field produced by the magnet around it. Now if you are going to put a magnetic needle near to the bar magnet you will see the needle points towards a direction. Now if you are going to move the needle around the bar magnet it will see that the needle is also changing its direction. The reason of this phenomenon is due to the attraction of magnet and the presence of magnetic field. As the magnetic needle is shifted to a new place it will change its orientation with 4

5 the magnetic field. If you make an experiment in this context you will see the following conditions illustrated in the figure below. Earth and its Relation to Magnetism: Now when you have the basic understanding of magnets and magnetic fields, lets plug into this concept with the Earth. If you look at a compass you will observe that it always points towards the same direction. Now question may arise why is it so? Well, the answer is simple. Along with several characteristics of earth, magnetism is one of the important one. It is assumed that our earth act like a giant bar magnet. The reason behind the origin of this character is presence of liquid outer core of the earth. In the outer core a huge volume of 5

6 materials is constantly in rotatory motion due to density difference resulted into formation of convection current (circulatory motion of the materials from high density region to low density region). This convection current gave birth to the magnetic property of the earth. The reason behind the origin of this character is presence of liquid outer core of the earth. In the outer core a huge volume of materials is constantly in rotatory motion due to density difference resulted into formation of convection current (circulatory motion of the materials from high density region to low density region). This convection current gave birth to the magnetic property of the earth. If you relate the concept of creation of magnet from the raw iron you will easily understand that the convection current is making continuous and systematic orientation of all the magnetic properties existing in the outer core in the form of different metals (mainly iron, nickel, cobalt etc. in this context). Now if our earth has magnetic property then it must be associated with magnetic fields. Yes, indeed. The magnetic fields of the earth run from the magnetic north pole and points towards the magnetic South Pole. If you will see a magnetic needle or compass, it generally coloured in red and blue on its two ends. The red one is called north seeking pole while the blue is known as south seeking pole. Once you hold a compass you will see it will always align itself 6

7 in the direction because it s aligning itself with the earth s magnetic field. Earths geographic poles are the two points of the rotating earth where axis intersects with it. On the contrary geomagnetic poles of the earth are away from the earth s geographic pole. This difference is known as magnetic declination (about 800 km away from the geographic poles currently). Technically, it is the angle between the earth magnetic meridian (imaginary vertical plane enclosing magnetic north and south) and geographic meridian (imaginary vertical plane enclosing geographic north and south). In the past it was observed that number of times the magnetic poles of the earth changes it position in a relatively small period (known as magnetic reversal). Hence it can be said that as the compass is pointing towards the north that means it must be attracted by the opposite magnetic pole of the earth. 7

8 Effect of Earth's Magnetic Field: The earth s magnetic field where its interacts with the suns electromagnetic solar wind is known as earth s magnetosphere. The shape of the magnetic field constantly shaped and reshaped by big solar storms caring solar plasma. As most of the time it s observed that the electromagnetically charged particles in majority are deflected (and human life is possible on earth) by the field but some of them are entered in the magnetic field. Once it interacts with atmospheric oxygen and nitrogen molecules resulted into cosmic lights in the night sky knows as Aurora in the polar region. 8

9 Recent study shows that the earth s magnetic field is changing at a relatively faster rate in the recent geological past that indicates another reversal in the coming geological time. If you are thinking about the effect of magnetic reversal on humans, well, there is no known extreme event causes magnetic reversal, but it surely will interfere with the electrical power grids and can cause power related issues. Dr. Tathagata Ghosh M.Sc. (Geography) Ph.D 9