Magnetism Study Material for IIT JEE
Magnetism is a class of physical phenomena that includes forces exerted by magnets on other magnets. It has its origin in electric currents and the fundamental magnetic moments of elementary particles.
Now we answer the question what is magnetism? Magnetism is the force by which the objects are attracted or repelled by one another. Usually these objects are metals such as iron. Besides iron, other materials that are easily magnetized when placed in a magnetic field include nickel and cobalt. Magnetism is a force of attraction or repulsion that acts at a distance. It is due to a magnetic field, which is caused by moving electrically charged particles. Iron is not the only material that is easily magnetized when placed in a magnetic field; others include nickel and cobalt.
Magnets can also be formed and such magnets are called electromagnets. A simple electromagnet is formed with a battery and copper wire coiled around a metal rod such as a nail. There is evidence that there is an electrical basis for magnetism.
Pierre de Mari court checked angles pointed out by an iron rod placed at various points of a natural magnet. He found that the directions were in such a way that they rounded the sphere and passed through two points diagonally opposite, which he called the ends or poles of the magnet. Later experiments showed that every magnet, regardless of its shape, has two poles, called north and south poles, that exert repulsive as well as attractive forces on other magnetic poles just as electric charges exert forces on one another.
Later William Gilbert extended de Mari court’s experiments to a variety of materials. Using the fact that a iron rod orients in some preferred directions, as per his hypothesis Earth itself is a large permanent magnet. Further a Torsion Balance was used for experiments and it was postulated that the force exerted varies inversely with the square of distance between them.
Magnetic Poles, Forces, and Fields
Magnetic Poles: Every magnet has two poles. The poles are the points in a magnet where the magnetic strength is at its peak. These poles are called the north and the south poles or the north seeking and south seeking poles. When a magnet is suspended or hung somewhere the magnet lines up in a north - south direction. As we know that the like charges repel and the unlike charges attract, so when the North Pole of one magnet is kept close to the north pole of another magnet, the poles are repelled. When the south poles of two magnets are placed near one another, they also are repelled from one another. When the north and south poles of two magnets are placed near one another, they attract each other.
The attraction or repulsion of two magnets towards one another depends on how close they are to each other and how strong the magnetic force is within the magnet. The further apart of the magnets are the less they are attracted or repelled to one another.
Note: Even when a magnet is broken into pieces each broken piece has its own north and South Pole.
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Magnetic Field: The imaginary lines of flux originating from moving or spinning electrically charged particles constitute the magnetic field. For example the spin of a proton and the motion of electrons through a wire in an electric circuit constitute magnetic fields. It is undoubtedly a special property of space. All materials are influenced to some extent by a magnetic field. Most materials do not have permanent moments. Some are attracted to a magnetic field, others are repulsed by a magnetic field while others have a much more complex relationship with an applied magnetic field. Substances that are negligibly affected by magnetic fields are known as non-magnetic substances. They include copper, aluminium, gases and plastic. Even pure oxygen exhibits magnetic properties when cooled to a liquid state.
Magnetic Force: The magnetic field of an object can create a magnetic force on other objects with magnetic fields. When a magnetic field is applied to a moving electric charge, such as a moving proton or the electrical current in a wire, the force on the charge is called a Lorentz force.
When two magnets or magnetic objects are close to each other, there is a force that attracts the poles together. Attraction always occurs between unlike poles. Except iron, magnets also attract nickel and cobalt.
When two magnetic objects have like poles facing each other, the magnetic force pushes them apart. Magnets might also repel diamagnetic materials
Magnetic and electric fields
There is a close relation between the magnetic and electric fields. They are similar as well as different.
Electric charges and magnetism similar
The poles of a magnet behave in the same way as the electric charges. The positive (+) and the negative (-) electrical charges attract each other and so do the North and the South Poles in a magnet. In electricity like charges repel, and in magnetism like poles repel.
Electric charges and magnetism different
The magnetic field is a dipole field as every magnet has exactly two poles. But in electricity, a positive (+) or a negative (-) charge can exist independently. Electrical charges are called monopoles, since they can exist without the opposite charge but a single magnetic pole can never be isolated.
The JEE aspirants can know how to study magnetism and electricity for jee with the help of online tutorials provided by askIITians. You may also consult the Model Papers to get an idea about the types of questions asked.