Magnetic fields

Magnetic Fields

If you are outside on a dark night in the middle to high latitudes, you might be able to see an aurora, a ghostly  certain”of light that hangs down from the sky. This curtain is not only located it may be several hundred kilometers high and several thousand kilometers long, stretching around Earth in an arc. However, it is less than 1 …

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Keepers

Keepers A bar magnet tends to become weaker with age, owing to self-demagnetization. This is caused by the poles at the ends of the magnet which tend to reverse the direction of the atomic dipoles inside it. In order to prevent this, bar magnets are stored in pairs, with their opposite poles adjacent and with small pieces of soft …

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Magnetic shielding

Magnetic shielding The magnetic field near a soft-iron bar placed horizontally in a N-S direction is shown in Fig. 31.17. This map was obtained by the compass-needle method. The earth’s magnetic flux appears to be drawn into the iron and concentrated through it. Iron is therefore said to be more permeable to magnetic flux than air is, or …

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To plot the magnetic flux pattern near the base of a magnetized iron pillar

To plot the magnetic flux pattern near the base of a magnetized iron pillar If the compass needle method is used to plot the magnetic flux pattern on the floor near the base of a vertical magnetized iron pillar a map similar to that shown in Fig. 31.15 (c) is obtained. Note that a neutral point occurs south …

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Magnetization of iron and steel used in building construction

Magnetization of iron and steel used in building construction Vertical steel pillars used in the construction of buildings are invariably found to be magnetized. This occurs owing to the induction by the vertical component of the earth’s magnetic flux density. Similarly, steel joists lying horizontally in the magnetic meridian become magnetized by the horizontal component. In such …

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Magnetic phenomena explained by the domain theory

Magnetic phenomena explained by the domain theory (I) Demagnetization Anything which disturbs the dipoles in the domains and enables them to settle down back in their preferred directions will weaken or destroy the magnetism of the magnet as a whole. Mechanical vibration can have this effect, and so also will a rise in temperature, since this is accompanied …

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Ferromagnetism. The domain theory of magnetism

Ferromagnetism. The domain theory of magnetism In some materials, of which iron, steel, and certain alloys are outstanding examples, the atomic magnets or dipoles do not act independently as in paramagnetic substances but small groups interact with one another so that their magnetic axes spontaneously line up together in a certain preferred direction. Groups such as these are described …

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Paramagnetism

Paramagnetism In other materials there are unbalanced electrons so that the individual atoms or molecules act like very tiny magnets. In the absence of an external magnetic field these molecular magnets are arranged at random, giving no resultant magnetic effect to the material as a whole, but if a magnetic field is applied the molecular magnets become partially aligned …

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Diamagnetism

Diamagnetism In many materials there are equal numbers of electrons spinning and orbiting in opposite directions so that, in the absence of some external magnetic field, their effects cancel out. If, however, a magnetic field is applied the electron orbits are very slightly disturbed by electromagnetic induction (page 484). This very slightly weakens the field inside the material giving …

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