A freely suspended bar magnet always comes to rest in a north-south direction. Neutral points are obtained on the magnetic field of a magnet which is due to the combined effects of its magnetic field and earth’s magnetism. This note provides us the information about terrestrial magnetism, magnetic meridian and geographical meridian and magnetic elements of earth's magnetic fields.
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.
Evidences of terrestrial magnetism
A freely suspended magnet always point N-S direction by the influence of terrestrial magnetism on it.
Some iron ores possess magnetism, which may be due to the effect of earth’s magnetism.
Angle of declination and angle of dip are due to the effect of earth’s magnetism.
Neutral points are obtained on the magnetic field of a magnet which is due to the combined effects of its magnetic field and earth’s magnetism.
Earth's Magnetic Field
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:
There is a permanent magnet inside the earth. This idea is ruled out. This is because the earth’s interior is at very high temperature and in this state nothing is magnetic.
Earth’s crust contains magnetic substances, which may have produced the earth’s magnetism. This idea was also rejected because the earth’s crust does not contain sufficient magnetic substances.
According to the latest theory, the magnetic field of the earth is caused by the magnetic current circulating in its core due to convection currents, arising from radioactive heating inside the earth.
Magnetism meridian and Geographic meridian
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.
Magnetic elements of earth’s magnetic fields
The quantities that are required to specify the magnetic field of the earth completely is called the magnetic elements of the earth.
Elements of earths magnetic field
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.
Things to remember
A freely suspended bar magnet always comes to rest in a north-south direction.
Angle of declination and angle of dip are due to the effect of earth’s magnetism.
Neutral points are obtained on the magnetic field of a magnet which is due to the combined effects of its magnetic field and earth’s magnetism.
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.
It includes every relationship which established among the people.
There can be more than one community in a society. Community smaller than society.
It is a network of social relationships which cannot see or touched.
common interests and common objectives are not necessary for society.
Videos for Earth’s Magnetic Field
Magnetic Dip
Magnets & Magnetism
Terrestrial Magnetism - Earth's Magnetic Field - Science
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 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.