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EARTH'S MAGNETIC FIELD - AN INTRODUCTION

   Like a bar magnet, Earth also has a magnetic field tilted 11° from the spin axis. In 1835, Carl Friedrich Gauss measured the Earth’s magnetic field strength. The Earth’s magnetic field intensity is strong when the field is vertical to the surface ( in the poles) and the intensity is weak when the field is horizontal to the surface (in the equator). It is not a short range field but it extends beyond the Earth's atmosphere and the strength of the magnetic field is weak so it is measured it in terms of gauss.   Earth has a non-dipolar magnetic field – The north pole and south pole are not in exact opposite directions.


   https://www.livescience.com/21668-why-earth-magnetic-field-wonky.html

Origin:

  • The earth’s magnetic field is not due to the magnet present in the core. 
  • Earth’s core is made of iron whose curie temperature is about 770° C, but Earth’s core hotter than that, so iron loses it’s magnetic property. 
  • We know that where there is current flow, a magnetic field is also associated with it. 
  • Inside the Earth’s core molten metallic fluid flows from one place to the other forming a current loop. This gives rise to the Earth’s magnetic field. 
  • It's magnitude varies over the surface of the earth in the range of 0.3 to 0.6 gauss. 
  • The earth’s magnetic field is estimated to be 3.5 billion years old through paleomagnetic field.

           Dynamo  Effect :-

               Another reason for the presence of earth’s magnetic field is dynamo effect.

  • The outer core of the Earth is made of molten iron and the inner core comprises of solidified elements.
  • Due to the rotation of Earth and convection electric currents are created in the core which leads to the magnetic field which is called dynamo effect.
  • It seems that there is a relation between magnetic field and the rotation of earth.
  • An evidence for this can be explained by comparing our Earth with it’s twin planet Venus.
  • We know that the size of Earth and Venus are almost equal and both it’s cores are made of iron.
  •  But Venus has a rotation period of 243 Earth days, so the rotation is very slow for Venus when compared to the Earth.
  • Due to this, Venus doesn’t have magnetic field while the Earth has it.

    https://www.nasa.gov/vision/earth/lookingatearth/29dec_magneticfield.html

    Facts on magnetic poles:

      Location :-

  • The magnetic North pole is present near the geographical South pole and the magnetic South pole is present near the geographical north pole. 
  • When a sailor uses a compass, the needle is attracted towards the magnetic south pole, so he will get the direction of the geographic north pole.

      Field reversal :-

  • The magnetic dip pole is not stationary always, an observation states that north pole moved upto 40 kilometers per year. 
  • When the magnetic field strength reaches zero, and then starts increasing the polarity of magnetic field will change. This is called as reversal of earth’s magnetic field. 
  • It is a rare phenomenon and the researchers have reported that in the past 71 million years, only 171 magnetic field reversals has taken place. 
  • The period for a reversal is unknown, but it can last up to 10000 years. The last geomagnetic reversal occurred 7,80,000 years ago.

    Applications:

  •   When the particles from the solar wind interacts with the terrestrial magnetic field, we can see the beautiful aurora phenomenon near the poles. 
  •  Animals and Birds make use of the Earth’s magnetic field to detect the direction in which they move during migration. They have a magnetic map in their head which sense the magnetic particles. 
  • For example, the loggerhead turtles have natural compasses which is used to navigate along the migrating direction. 
  • The magnetosphere protects the Earth's organisms from harmful solar radiations.

      References:

  • https://web.ua.es/docivis/magnet/earths_magnetic_field2.html
  • https://www.nasa.gov/vision/earth/lookingatearth/29dec_magneticfield.html
  • http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/MagEarth.html

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