Magnetic Field Lines

Key Concepts

• Magnetic field lines due to a pair of magnets.
• Neutral point and uniform magnetic fields.

Introduction: 

When two bar magnets are placed close to one another, they produce a different magnetic field pattern. The pattern depends upon the orientation of a bar magnet w.r.t the other. In this session we will be looking at these different patterns generated by a pair of bar magnets. 

Explanation: 

Magnetic field due to a pair of bar magnets: 

When two magnets are brought close to each other their magnetic lines of force interact with each other and get modified to point in the direction of the resultant magnetic force (field). 

Magnetic field lines due to unlike poles: 

When the unlike poles of two magnets are brought closer together, their magnetic lines of force seem to merge and form a new pattern showing the resultant field. 

The resultant field in between the magnets points from the north pole towards the south pole.  

Hence, the magnets experience an attractive force and move towards each other. 

In the middle of the two unlike poles, a uniform magnetic field is generated with equally spaced parallel magnetic field lines. 

However, as we move outwards, the magnetic lines of force curve out, making the field non-uniform. 

Magnetic field lines due to a pair of like poles: 

When the unlike poles of two magnets are brought closer together, their magnetic lines of force seem to diverge from each other and form a new pattern showing the resultant field. 

No magnetic lines of forces of either magnets merge with each other. 

The resultant field has the field lines of either magnets pointing away from each other. 

Hence, the magnets experience a repulsive force and move away from each other. 

In the middle of the two like poles, no magnetic field exists. This point is called the neutral point. 

At the neutral point the two magnetic fields cancel the effect of each other resulting in a zero resultant field. 

Questions and Answers: 

1. How many neutral points are there in the magnetic field shown below? Identify them. 

Answer: 

There are two neutral points in the magnetic field shown. 

2. How many regions of uniform magnetic fields are there in the magnetic field shown below? Locate them in the field. 

Answer:  

There are two regions of uniform magnetic fields in the magnetic field below. 

Summary:

• A compass needle points in the direction of magnetic force exerted on it due to the presence of the bar magnet.
• When two magnets are brought close to each other their magnetic lines of force interact with each other and get modified to point in the direction of the resultant magnetic force (field).
• When the unlike poles of two magnets are brought closer together, their magnetic lines of force seem to merge and form a new pattern showing the resultant field.
• In the middle of the two unlike poles, a uniform magnetic field is generated with equally spaced parallel magnetic field lines.
• When the unlike poles of two magnets are brought closer together, their magnetic lines of force seem to diverge from each other and form a new pattern showing the resultant field. No magnetic lines of forces of either magnets merge with each other.
• In the middle of the two like poles, no magnetic field exists. This point is called the neutral point.
• At the neutral point the two magnetic fields cancel the effect of each other resulting in a zero resultant field.