We are all familiar with ferromagnetism or the magnetic behavior of substances s

Question

We are all familiar with ferromagnetism or the magnetic behavior of substances such as iron, nickel, and cobalt. These materials align the magnetic moments of their own atoms with an externally imposed magnetic field. In other words materials exhibiting ferromagnetism become magnetic themselves when exposed to an external magnetic field. Less familiar are paramagnetic and diamagnetic materials. Paramagnetic materials may become magnetized but do not retain a magnetic field as say an iron nail might. Diamagnetic materials actually align their internal magnetic moments in opposition to an externally imposed magnetic field.

Maxwell’s equations are sufficient to describe the magnetic fields of refrigerator magnets, and even the intense fields required to levitate diamagnetic objects within high magnetic field laboratories. The situation becomes rapidly more complex when the materials and fields involved begin to self interact.It is thought that the Earth generates magnetic fields through a combination of convection of a molten core and the rotation of the planet. We have not successfully been able to simulate this process in part because the system is self- interacting, or non linear. This occurs because magnetic fields generated by currents in one portion of the Earth’s interior begin to exert forces on and alter the motion of other convective currents elsewhere in the system.

To complete this discussion activity:

Do your own internet research, and then write an initial response to the following three discussion prompts. Post your response to the discussion board.

What is the source of the Earth’s magnetic field? In your response be sure to use the terms dynamo theory, inner core, outer core, convection, and rotation.

The Earth’s magnetic field undergoes periodic reversals. How was this discovered, and by whom? What is the current best theory of its cause?

How does the magnetosphere interact with charged particles in the solar wind? What happens to a planet without a planetary magnetic field, e.g. Mars?

Explanation / Answer

Q.No.1The earth's magnetic field is similar to that of a bar magnet tilted 110 from the spin axis of th Earth. The problem with that picture is that the Curie temperature of iron is aboout 7700 . The Earth's core is hotter thatn that and therefore not magnetic. So, how did the Earth get its magnetic field?

Magnetic fields surround electric currents, so we surmise that circulating electic currents in the Earth's molten metalic core are the origin of the magnetic field. A current loop gives a field similar to that of the earth. The magnetic field magnitude measured at the surface of the Earth is about half a Gauss and dips toward the Earth in the northern hemisphere. The magnitude varies over the surface of the Earth in the range 0.3 to 0.6 Gauss.

The Earth's magnetic field is attributed to a dynamo effect of circulating electric current, but it is not constant in direction. Rock specimens of different age in similar locations have different directions of permanent magnetization. Evidence for 171 magnetic field reversals during the past 71 million years has been reported.

Although the details of the dynamo effect are not known in detail, the rotation of the Earth plays a part in generating the currents which are presumed to be the source of the magnetic field. Mariner 2 found that Venus does not have such a magnetic field although its core iron content must be similar to that of the Earth. Venus's rotation period of 243 Earth days is just too slow to produce the dynamo effect.

Convection drives the outer-core fluid and it circulates relative to the earth. This means the electrically conducting material moves relative to the earth's magnetic field. If it can obtain a charge by some interaction like friction between layers, an effective current loop could be produced. The magnetic field of a current loop could sustain the magnetic dipole type magnetic field of the earth. Large-scale computer models are approaching a realistic simulation of such a geodynamo.

Q.NO.2.

In a recent study, scientists from the Ecole Normale Supérieure and the Institut de Physique du Globe de Paris, both in Paris, have proposed a general mechanism that provides a simple explanation for field reversals. In their model, small fluctuations in convective flow in Earth’s core can push the planet’s sensitive magnetic system away from one pole toward an intermediate state, where the system becomes attracted to the opposite pole.
Current best theory is regarded as dynamo effect for the producing the magnetic field.

Q. No. 3....when the charged particles (ion comes from sun ) comes in the magnetosphere. that charged particle experience the magnetic force and form circular loop.The solar wind is a stream of ionized gases that blows outward from the Sun at about 400 km/second and that varies in intensity with the amount of surface activity on the Sun. The Earth's magnetic field shields it from much of the solar wind. When the solar wind encounters Earth's magnetic field it is deflected like water around the bow of a ship.

when there is no magnetic field on the planet then planet will be dried because of solar flare.our Earth escaped this fate because its strong magnetic field deflects the wind. However, a debate has arisen over whether a magnetic field is any kind of shield at all.

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