Magnetic Pole: Definition, Features, Magnetic Pole of Earth

Magnetic pole or poles of a magnet is the region at the ends of a magnet where the magnetic field is strongest. Magnetic Poles produce magnetic flux and thus are referred to as the flux source. All magnets have two poles, known as the north pole and the south pole.

• Poles of a magnet have the property to attract small pieces of magnetic materials
• The strength with which a magnetic pole attracts is known as Pole strength
• More the pole strength, more is the power of a magnet
• When a magnet is suspended freely, the north pole always points towards the geographical north, and the south pole points toward the geographical south of the earth

Read More: Semiconductor Electronics Important Questions

Key Terms: Magnets, magnetic pole, Magnetic Flux, compass, magnetic field lines, Earth's magnetic pole, magnetic field, magnetic axis, iron, nickel, cobalt, steel

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Magnetic Pole

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The magnetic pole is the region at the end of the magnet where the external magnetic field is strongest. A magnet comprises two poles namely the north pole and the south pole.

• The line joining the north pole and south pole of a magnet is called the magnetic axis.
• A vertical plane passing through the magnetic axis of a magnet is called magnetic meridian.
• A pole of the magnet is known as a monopole magnet, which is a hypothetical elementary particle.
• Magnetic poles always exist in pairs.
• If a magnet is cut into two pieces it will result in two complete magnets each having both north, as well as south pole.

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Magnets

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Any physical object that has the ability to attract or generate a magnetic field is known as a magnet. Magnets have the ability to attract ferrous objects like iron, nickel, cobalt, and steel. 

• A bar magnet is the most common example of a magnet that all of us have seen in our daily lives.
• The bar magnet is nothing but a regular cuboid that can attract ferrous objects like iron and steel.
• It consists of the North and the South Poles in different colors.
• Commonly, the blue end is the south pole and the red end is the north pole.
• A bar magnet is also called magnetic dipole.

A magnetic compass needle is a most commonly used device to navigate and know about the magnetic field direction. It helps sailors to find their way. The magnetic needle contains a horizontal needle pivoted at the centre and ends of this point to the north and south pole depending upon the location and direction.

Read More: Moving Charges and Magnetism

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Properties of Magnets

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The important properties of magnets are:

• Unlike poles of two magnets attract each other and, like poles or similar poles of two magnets repel each other.
• Breaking a magnet does not result in splitting its north pole and south pole; instead it creates two new respective poles for each magnetic piece.
• Magnets have the properties of induction.
• When a piece of magnetic material is brought near a bar magnet without any physical contact, then the magnetic material acquires the property of magnetism.
• Such a type of magnetism is called induced magnetism.
• Magnetic field lines of a bar magnet always travel from the north pole to south pole outside the magnet.
• But it travels from the south pole to the north pole inside the magnet.
• Repulsion is the surest test for distinguishing between an iron piece and a magnet.
• North pole of a magnet can be identified by bringing another magnet having its pole marked as the north pole and the south pole.

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Magnetic Poles of Earth

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Earth also has its own magnetic field. Earth’s magnetism is assumed due to a huge bar magnet with its axis inclined at an angle of \(11.3^{\circ}\) west of the axis of rotation of earth.

• The pole near the geographic north of the earth is called the north magnetic pole.
• The magnetic north pole of earth is located at a latitude of \(79.74^{\circ}N\)  and a longitude of \(71.8^{\circ}W\), a place near south Canada.
• It is a point on the surface of the Northern Hemisphere of the earth at which the magnetic field of Earth vertically points downwards.
• The pole near the geographic south of the earth is called the south magnetic pole.
• The magnetic south pole of the earth is at \(79.74^{\circ}S\)  and \(108.22^{\circ}E\), in Antartica.
• It is the fixed point on the southern hemisphere of the Earth where the geomagnetic field lines direct vertically upwards.
• These two poles of the earth are known as Earth’s magnetic poles or Geomagnetic poles and the corresponding north and south pole of earth is also known as the geomagnetic north pole and the geomagnetic south pole respectively.

Read More: Magnetism and Gauss’s Law

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Magnetic Flux

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Magnetic flux can be simply defined as the total number of magnetic flux lines passing through a close surface area. It measures the total magnetic field passing through a given surface area. The area can be of any size or orientation. 

The formula for magnetic flux:

\(\phi_B= \vec B.\vec A=BA cos\theta \)

Where, 

• \(\phi_B\) = magnetic flux
• B = magnetic field
• A = surface area
• \(\theta\) = angle at which the field lines pass through the given surface area

Magnetic flux is generally measured in weber while the standard unit is volt-seconds.

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Magnetic Moment

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Magnetic Moment or magnetic dipole moment can be defined as the measure of an object’s tendency to align with a given or applied magnetic field.

• It is a vector quantity that connects an object’s torque to a magnetic field.
• The magnetic moment is measured in Amp-metre² (Am²).

Mathematically, it is expressed as:

\(\vec \tau = \vec m \times \vec B\)     or   \(\tau= mBsin\theta\)

Where, 

• \(\tau\) = torque applied on the dipole
• m = magnetic moment
• B = external uniform magnetic field
• \(\theta\) = angle between magnetic dipole moment and uniform magnetic field

Magnetic dipole moment is also given by:

\(m=q_m \times2l\)

Where,

• q_m = pole strength of either pole of the magnet
• 2l = distance between the two poles of the magnet

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Things to Remember

• The magnetic pole or pole of the magnet is the region at the end of the magnet where the external magnetic field is strongest. 
•  A magnet comprises two poles namely the north pole and the south pole.
• The two ends of the magnet that have the strongest magnetic field are known as the magnetic poles. 
• The bar magnet is a regular cuboid that can attract ferrous objects like iron and steel. 
• Unlike poles of a magnet attract each other and like poles of a magnet repel each other.
• Earth has its own north pole and south pole.
• At the north pole, the north hand of the compass points downwards and at the south pole, the south hand of the compass points upwards.
• Magnetic Flux can be calculated by the formula- \(\phi_B=BA cos\theta \)
• The formula to calculate magnetic moment is \(\vec \tau = \vec m \times \vec B\) and \(m=q_m \times2l\).