For example, closer you are to the Earth, stronger the force. Similarly, a magnet sets up a magnetic field in its surrounding space in which it magnetically affects any other magnetic material. The strength is represented by the density of the magnetic field lines. Magnetic field lines are closed curves leaving from North pole and entering the South pole when you follow them on the outside the magnet.
A compass, which is a small magnet itself, lines up parallel to the magnetic field lines at the point it is placed. The tip of the arrow is the North magnetic pole, and its end is the South magnetic pole. The building blocks of magnets are atoms, which are small tiny magnets. We will see later that, the motion of electrons moving electric charge is the fundamental reason of magnetism.
For practical purposes we can focus on a cluster of atoms, called magnetic domains that are aligned in a specific direction. Each domain may consist of billions of aligned atoms. On the other hand, the domains of a magnet or a magnetized iron are all aligned in s specific direction.
Domains are separated from the adjacent domains by domain walls. In general, alignment within a domain is the same for all atoms of that domain. These properties make electromagnets useful for picking up scrap iron and steel in scrapyards. The magnetic field around an electromagnet is just the same as the one around a bar magnet. It can, however, be reversed by reversing the current turning the battery around. Electromagnets When an electric current flows in a wire, it creates a magnetic field around the wire.
Spinning like tops, the electrons circle the nucleus , or core, of an atom. Their movement generates an electric current and causes each electron to act like a microscopic magnet. In most substances, equal numbers of electrons spin in opposite directions, which cancels out their magnetism. That is why materials such as cloth or paper are said to be weakly magnetic.
In substances such as iron , cobalt , and nickel , most of the electrons spin in the same direction. This makes the atoms in these substances strongly magnetic—but they are not yet magnets. To become magnetize d, another strongly magnetic substance must enter the magnetic field of an existing magnet. The magnetic field is the area around a magnet that has magnetic force. All magnets have north and south poles.
Opposite poles are attracted to each other, while the same poles repel each other. When you rub a piece of iron along a magnet, the north-seeking poles of the atoms in the iron line up in the same direction. The force generated by the align ed atoms creates a magnetic field. The piece of iron has become a magnet. Some substances can be magnetized by an electric current. When electricity runs through a coil of wire, it produces a magnetic field. The field around the coil will disappear, however, as soon as the electric current is turned off.
Geomagnetic Poles. The Earth is a magnet. The geomagnetic pole s are not the same as the North and South Poles. Strangely, the magnetic records of rocks formed at the same time seem to point to different locations for the poles. Thus, the plates on which the rocks solidified have moved since the rocks recorded the position of the geomagnetic poles.
These magnetic records also show that the geomagnetic poles have reversed—changed into the opposite kind of pole—hundreds of times since the Earth formed. Therefore, it can be a useful tool for helping people find their way around. The north end of a magnet points toward the magnetic north pole. Solar wind , charged particles from the sun, presses the magnetosphere against the Earth on the side facing the sun and stretches it into a teardrop shape on the shadow side.
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