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  • Complete Physics Course - Class 11
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The Bar Magnet

 

Table of Content

 

Introduction to The Bar Magnet

A bar magnet is the simplest form of magnets which is rectangular in shape and has a magnetic field around it. It is usually made of ferromagnetic materials (elements that have naturally magnetic fields like cobalt, iron and nickel). The bar magnet is also known as Permanent The Bar MagnetMagnet because it can retain its magnetic field for some time in the absence of any magnetic field.

Before understanding how a bar magnet works we need to understand the concept of magnetic field lines.

Magnetic field lines: Magnetic field lines are created by moving point charges in an electric charge carrying conductor. They are imaginary line of force around a magnet that attract or repel other ferromagnetic materials. When a ferromagnetic material is placed inside a magnetic field, they are heated to a certain temperature after which they are permanently magnetized. A magnet has normally two poles (a) North Pole and (b) South pole. By convention it is believed that magnetic field lines flow from North Pole to South Pole.
 

Working of a Bar Magnet

From the figure given below it can be clearly understood that the magnetic field lines inside a bar magnet is the strongest, while the external strongest magnetic lines are near the poles. A magnetic north pole will attract the south pole of another magnet and repel the north pole of another magnet

Working of a Bar Magnet

Tracing of Magnetic Field lines around a Bar Magnet

The simplest way to trace a magnetic field lines around a bar magnet is by using a compass. The needle of the compass is a magnet. The end which points towards the south is called the South Pole, while the other point is called the north pole. To trace the magnetic field lines around a bar magnet, place the bar magnet in a piece of paper. Next draw a dot anywhere near the magnet and place the compass over the dot. Observe the direction of the compass needle and draw a dot at the North Pole and South Pole of the needle. Repeat the procedure for different position. Connect the dots and mark the direction of the compass with an arrow.

Compass placed at different position near the bar magnet

Fig: Compass placed at different position near the bar magnet

Tracing of the magnetic field lines in a paper

Fig: Tracing of the magnetic field lines in a paper

Classification of Magnets

Magnets are classified into two types:

  • Permanent Magnet

  • Temporary Magnet


Permanent Magnets

A Permanent Magnet is the one which can retain its Magnetic properties for a long period of time, whereas a temporary magnet loses its magnetic properties once it is removed from the magnetic field. Example of a permanent magnet is a bar magnet. A magnetic material is permanently magnetized when it is placed in an externally strong magnetic field line created by current carrying conductor. After a certain temperature, when the magnet is heated, it is permanently magnetized.


Temporary Magnets

A temporary magnet does not retain its magnetic properties once the magnetic field is removed. This is because when the magnetization is stopped, the atomic arrangements inside the material is aligned in different direction. It is obvious that when the atomic arrangements are in the same direction they act as a larger domain and hence create a strong magnetic field rather than the single domain. A good example of temporary magnet is the electro magnets. Electro magnets are magnets that are temporarily made using electric current. This study of relation between electricity and magnetism is known as Electromagnetism.

A good example of electromagnets is a Solenoid. A solenoid in physics means a long loop of wire tightly wrapped into helix around a metallic core. 

Temporary Magnets

In the above given figure, a thin long wire is wrapped around metallic core, and each ends of the wire is connected to an electrical source. The direction of the north pole and the south pole is determined by the right hand grip rule. This rule says that if we curl the fingers of our right hand in the direction of the current, then the direction of the thumb gives the direction of the north and South Pole.

More the number of turns around the core, more strong is the magnetic field.
 

Characteristics of a Bar Magnet

  • When a bar magnet is suspended freely in the air it always points in the north-south direction due to earth’s giant magnetic field.

  • The magnetic field lines of a bar magnet are strong near the poles.

  •  A bar magnet is the most widely used magnet to illustrate the properties of magnetism and trace the magnetic field lines.

  • When a bar magnet is cut into two pieces, instead of getting destroyed itself, two new magnets are formed with two poles north pole and south pole
     

Uses of a Bar Magnet

  • Bar magnets are used in Fridge Magnets.

  • They are used in guitar. They are wrapped with a coil in a guitar to create a magnetic field. Thus the vibration in the strings is detected by the coil and this creates a voltage which in turn produces the perfect sound.

Uses of a Bar Magnet

Conclusion

Bar magnet is a permanent magnet which is rectangular in shape and creates an imaginary magnetic field lines around it in such a way that the magnetic force is strong near the poles. It is a permanent because it retains its magnetism for a period of time, even if there is no magnetic field present externally. The process by which a magnetic material can be made permanent or temporary magnets is known as Magnetization. Permanent magnets are made by placing the magnetic materials inside a very high external magnetic field for some time till it meets the criteria for being a permanent Magnet. While a temporary magnet is created by placing the magnetic material in a current carrying conductor. Once the electricity is removed, the material loses its magnetic properties.
 

Frequently Asked Question (FAQs)


Q1. What are the characteristics of Magnetic Field Lines?

Sol. Magnetic field lines are imaginary field lines around the magnet which helps us to determine the range of the magnetic force exerted by the magnet on other Ferro magnetic materials. The magnetic field lines are very strong near the poles and weak at the far distance.
 

Q2. Why are magnets shaped like a horseshoe?

Sol. Some magnets are shaped like a horseshoe because of the high magnetic flux at the end. The lifting power of a horseshoe is more than that of a simple rectangular bar magnet.


Q3. How does a magnet work?

Sol. A magnet has an imaginary magnetic field around it. Also a magnet has two poles a) North pole and b) South pole. When another magnetic material is brought near the magnetic field of the magnet, the north pole of the magnet attracts the south pole of the magnetic material.


Watch this Video for more reference
 


 

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The Bar Magne

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