Webers theory

Webers theory

1. Weber’s Theory of Magnetism

2. Outline 1- What is magnetism? 2- Types of magnet 3- Theories of magnetism 4- Weber’s theory of magnetism 5- Main points of Weber’s theory 6- Explanation of Weber’s theory

3. What is magnetism? It the force of attraction or repulsion due to electron arrangement. Magnetic forces are strongest at the poles. Magnets have two poles: North and South. When free to rotate, to come to rest pointing in a north south direction. Like magnetic poles repel. Unlike magnetic poles attract.

4. Types of magnet Natural magnet: known as lodestone which is a type of iron ore with magnetic properties. Artificial magnet: materials in which magnetic properties are produces artificially such as iron, cobalt, nickel steel. Temporary magnet: that loses their magnet properties easily and quickly such as soft iron.

5. Types of magnet Permanent magnet: which retain their properties. More longer and difficult to magnetize such as steel . Electromagnet: an electric current produces magnetic effects and a coil of wire carrying a current act as an electromagnet.

6. Theories of magnetism Basically there are two main theories of magnetism: 1- Weber’s theory 2- Domain theory

7. Weber’s theory of magnetism This theory was given by Weber in 1852. It was further modified by Ewing in 1890.

8. The basic assumption of this theory is that molecules of all substances are inherently magnets in themselves, each having a N and S pole. In unmagnetised state, it is supposed that these smaller molecular magnets lie in all sorts of haphazard manner forming more or less closed loop.

9. Main points of theory 1- Each and every molecule of a magnetic substance is a complete magnet in itself, having a north pole and a south pole of equal strength. 2- In an unmagnetised substance, the molecular magnets are randomly oriented such that they form closed chains. 3 - When the substance is magnetized, the molecular magnets are realigned so that north poles of all molecular magnets point in one direction and south poles of all molecular magnets point in the opposite direction.

10. 4 - When all the molecular magnets are fully aligned, the substance is said to be saturated with magnetism.

11. Explanation of Weber’s theory A magnetized material will have most of its molecular magnets lined up so that the north pole of each molecule points in one direction, and south pole faces the opposite direction. A material with its molecules thus aligned will then have one effective north pole, and one effective south pole, where a steel bar is magnetized by stroking.

12. When a steel bar is stroked several times in the same direction by the magnet, the magnetic force from the north pole causes the molecules to align themselves. During heating the magnetized specimen, molecular magnets acquire some kinetic energy. Some of the molecules may get back to the closed chain arrangement. That is why magnetism of the specimen would reduce on heating.

13. R eferences www.study.com www.slideshare.net www.tpub.com http:// apsacwestridge.edu.pk http://elementsofelectricalengineering.blogspot.com