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The earth’s magnetism is called terrestrial magnetism. Declination, dip and the horizontal component of earth’s magnetic field are elements of terrestrial magnetism which helps to locate correct direction.
A freely suspended bar magnet always comes to rest in a north-south direction. This shows that earth behaves as a huge magnet. The n-pole of a compass needle points towards geographical north showing that there is earth’s magnetic South Pole. Similarly, S-pole of the compass needle points towards geographical south showing that there is earth’s magnetic North pole.
The possible causes of earth’s magnetic field are given below:
The vertical plane passing through the axis of a freely suspended magnet at a place is called the magnetic meridian.
The vertical plane passing through a place and the geographical north and south poles is called the geographic meridian at that place.
The quantities that are required to specify the magnetic field of the earth completely is called the magnetic elements of the earth.
Angle of declination: The angle between the magnetic meridian and geographic meridian at a place is called angle of declination at that place.
Angle of dip or inclination: Angle of dip is the angle made by a freely suspended magnet at rest with the horizon.
The materials which are attracted by a magnet are called magnetic materials. The materials which are not attracted by a magnet are called non magnetic materials.
The magnetic field of a magnet is defined as the region around the magnet in which magnet or magnetic substance experiences a force The magnetic lines of force are the curves around the magnet along which a unit north pole would move if it was free to move.
The neutral point is the point where the earth's magnetic field and the field due to the bar magnet becomes equal and opposite making the resultant field zero. At this point, magnetic compass does not show any fixed direction.
It is also considered that the earth is a huge magnet in which North pole lies at geographical south pole and south pole lies at the geographical north pole. When a bar magnet is freely suspended, north pole of a bar magnet is attracted by earth's magnetic south pole as opposite poles attract each other and turns towards north pole.
The angle madeby the intersection of the line joining the magnetic north-south (magnetic meridian) and the line joining the geographical north-south (geographical meridian) at a place is called angle of declination of that place. It is necessary while flying airplane during nights as well as sailingships in the ocean.
The angle made by the freely suspended magnet with the horizontal axis called the angle of dip or angle of inclination.
To measure the angle of dip, dip circle is used.
The figure shows the angle of dip at the poles. Its value is 900at this place because south pole of the dip needle becomes perpendicular to the geographical north pole and vice versa.
The value of angle of dip at the magnetic equator is 00 and 900 at the magnetic north pole.
The maximum value of angle of dip on the earth's surface is 900 which is at the magnetic poles.
The angle of dip at Kathmandu is 420 means that a dip needle will be inclined to horizontal axis by 420 in Kathmandu.
The angle of declination in Kathmandu valley is 220E means that N-pole of horizontal compass needle will point 220 east to the geographical north and south direction.
|Angle of declination||Angle of dip|
|It is the angle between magnetic meridian and geographical meridian at a place.||It is the angle made by a freely suspended magnet with the horizontal.|
|Its maximum value is less than 900.||Its maximum value is 900.|
The component of earth's magnetic field along the horizontal direction is called the horizontal component of earth's magnetic field.
If a freely suspended needle has a angle of dip equal to 90o where in earth is it's position?
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