Earth – A Giant Magnet

Key Concepts:

• Earth – A Giant Magnet
• Neutral Points
• Effect of the magnetic field of the Earth

Introduction:

A compass needle gets deflected from its usual position only in the presence of a magnetic field around it or close to it. It is the magnetic field from any source that makes the compass needle deflect in a certain way depending upon the pole closer to it. However, a freely suspended bar magnet always points in the Earth’s north-south direction. In this section, we are going to find the reason for this. 

Explanation: 

Magnetic field of the Earth: 

A magnetic compass needle deflects and aligns itself in a specific direction only in the presence of a magnetic field. 

This means that our Earth has a magnetic field around itself and is a huge magnet. 

In fact, the Earth behaves as if it has a huge bar magnet placed at its center. 

The north pole of the compass needle points in the Earth’s geographic north direction. 

The south pole of the compass needle points in the Earth’s geographic south direction. 

The magnetic north pole of the compass needle is attracted towards the geographic north pole of the Earth. 

And the magnetic south pole of the compass needle is attracted towards the geographic south pole of the Earth. 

In fact, the Earth has two sets of poles viz., geographic (north and south) poles and magnetic (north and south) poles. 

The magnetic south pole lies closer to the geographic north pole and the magnetic north pole lies closer to the geographic south pole. 

Therefore, there are two axes viz., the geographic axis and the magnetic axis of the Earth, which make an angle of 11.5 degrees with each other. 

However, the magnetic poles of the Earth shift slightly all the time. 

As the Earth is a giant magnet, it has a magnetic field around it, wherein the magnetic field lines pattern resemble the bar magnet. 

The magnetic field lines emerge from the north magnetic pole and enter the south magnetic pole of the Earth. 

This magnetic field of the Earth originates from the convection currents formed due to the motion of molten iron and nickel in the Earth’s outer core. This is called the dynamo effect. 

Neutral points of a bar magnet in the Earth’s magnetic field: 

A neutral point in a magnetic field is that point where the magnetic field is zero and no lines of force pass through it. 

Case-1: When the north pole of a bar magnet points towards the Earth’s magnetic north pole: 

There are two neutral points formed in this case. At these points the magnetic field due to the bar magnet exactly cancels out the field due to the Earth. 

 

Case-2: When the south pole of a bar magnet points towards the Earth’s magnetic north pole: 

There are two neutral points formed in this case. At these points the magnetic field due to the bar magnet exactly cancels out the field due to the Earth. 

 

Effect of the magnetic field on the Earth: 

The Sun emits streams of charged particles called solar winds, which if comes in contact with living organisms can harm them. 

However, these solar winds are deflected by the Earth’s magnetic field. Hence, the living organisms on the Earth do not come in contact with it. 

The charged particles in the solar wind spiral towards the magnetic north and south poles. 

If these charged particles collide with the particles in the Earth’s atmosphere, they cause red and green lights, which spread across a large part of the sky, called the aurora. 

People living in higher (Sweden, Finland etc.) and lower (Tasmania, New Zealand etc.) latitudes can witness aurora borealis and aurora australis respectively. 

Questions and Answers: 

Question 1: In which direction does a compass needle not point when it is placed on the ground? 

1. In the direction of geographic north and south of the Earth 

2. In the magnetic north and south direction of the Earth 

3. In the direction of the magnetic field of the Earth at that point 

4. In the direction of the magnetic force due to the Earth’s magnetic field at that point. 

Answer: 

In the direction of geographic north and south of the Earth. 

Question 2: A compass needle was aligned in the Earth’s magnetic north-south direction. However, when a bar magnet is brought near to it, it turns to align itself according to the magnetic field of the bar magnet. Why? 

Answer:  

Initially the magnetic needle was only under the influence of the Earth’s magnetic field. However, when a bar magnet is brought near it, it experiences a stronger field as compared to the Earth’s magnetic field near it. Hence, it gets deflected according to the magnetic field of the bar magnet. 

Summary:

• A compass needle gets deflected from its usual position only in the presence of a
  magnetic field around it or close to it.
• ‘The Earth has a magnetic field around itself and is a huge magnet.
• ‘The Earth has two sets of poles viz, geographic (north and south) poles and magnetic
  (north and south) poles.
• ‘There are two axes viz,, the geographic axis and the magnetic axis of the Earth, which
  make an angle of 11.5 degrees with each other. However, the magnetic poles of the Earth
  shift slightly all the time.
• ‘The magnetic field of the Earth originates from the convection currents formed due to
  the motion of molten iron and nickel in the Earth’s outer core. This is called the dynamo
  effect.
• ‘There are two neutral points each formed when a bar magnet has its north pole towards
  the Earth’s magnetic north and its south pole towards the Earth’s magnetic north.
• If the charged particles in the solar wind collide with the particles in the Earth’s
  atmosphere, they cause red and green lights near the poles, which spread across large
  part of the sky, called the aurora.