Friday, February 19, 2010
Friday, January 8, 2010
Sunday, November 8, 2009
Ewings molecular theory of magnetism
Next we can talk about an important theory regarding electromagnetism.
If we break a magnet into two parts each parts become a magnet with a north pole at one end and a south pole at the other end. If we break it further, we observe the same behaviour. This will continue even if we break the magnet to its molecular level.
Each molecule of a magnetic substance is an independent magnet irrespective of whether the substance is magnetized or not. These tiny magnets are called molecular magnets.
In an unmagnetised state (fig(a)), the molecular magnets are in different orientation. Therefore the net magnetic effect is zero.In the magnetised state (fig(b)), these molecular magnets are arranged in an order. All the south poles are aligned in one direction, and the noth poles in the other direction. Therefore a strong magnetic field is created.
In general, perfect alignment of all the magnets in the entire magnet is difficult to obtain. When this condition is obtained it is called the point of saturation and magnetizing the magnet further cannot increase the strength of the magnet. These postulates are known as Ewings molecular theory named after the scientist who proposed them.
If we break a magnet into two parts each parts become a magnet with a north pole at one end and a south pole at the other end. If we break it further, we observe the same behaviour. This will continue even if we break the magnet to its molecular level.
Each molecule of a magnetic substance is an independent magnet irrespective of whether the substance is magnetized or not. These tiny magnets are called molecular magnets.
In an unmagnetised state (fig(a)), the molecular magnets are in different orientation. Therefore the net magnetic effect is zero.In the magnetised state (fig(b)), these molecular magnets are arranged in an order. All the south poles are aligned in one direction, and the noth poles in the other direction. Therefore a strong magnetic field is created.
In general, perfect alignment of all the magnets in the entire magnet is difficult to obtain. When this condition is obtained it is called the point of saturation and magnetizing the magnet further cannot increase the strength of the magnet. These postulates are known as Ewings molecular theory named after the scientist who proposed them.
Saturday, October 31, 2009
some basics on Electromagnetism
Introduction
In 1820, Hans Christian Oersted discovered that current carrying conductors produce a magnetic field around them. Later Michael Faraday showed that current can be induced in a conducting coil, when there is relative motion between coil and magnet. Thus electric current has a magnetic effect and changing magnetic fields can induce electricity.
Important properties of magnets
- Property of attraction:Magnets attracts small pieces of materials like iron, nickel, cobalt. The strength of the magnets are concentrated on the poles.
- Property of direction: a freely suspended magnet always align itself in the north- south direction. The pole which point towards the geographic north is called the north pole of the magnet. The pole which points towards geographic south is called south pole.
- Property of induction:A magnet can induce magnetism in substances like softiron, cobalt, nickel etc.
The next part of the lesson will be on Wednesday, 4th November 2009.
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