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Magnetism of Earth – What’s the cause?

Selwyn posted this Message: I was recently showing my grandchildren the effect on a compass needle by the magnetic field surrounding a magnet placed in opposition to the earth’s magnetic field – Magnetism 1.01 no? Their mother then asked me how is it that the earth has a magnetic field. I confidently answered that it was due to the central molten iron core of the earth acting as a magnet, and of course as we learned in Magnetism 1.1 68 years ago on of the ways of creating a magnet is a) by striking it several blows with a hammer while holding it in alignment with the earth’s N/S axis or b) heating it. In both cases this allows the atoms to move more freely and align themselves similarly with the axis. But that started me thinking: We know that heating ANYTHING applies energy to the atoms/molecules and this then causes them to display greater and more violent movement within the body of the material. If these molecules are so agitated, how can this identical phenomenon allow the molecule/atoms of the earth’s core to “settle down quietly” into a N/S configuration and remain so?

Answer:

The answer is not so simple. Nobody has actually drilled into the centre of earth. What we know is by analysing the seismic waves and the shockwaves.

The Earth’s magnetic field is believed to be generated by electric currents in the conductive material of its core, created by convection currents due to heat escaping from the core. However the process is complex, and computer models that reproduce some of its features have only been developed in the last few decades. (Wikipedia)

The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of highly conductive fluids. The Earth’s field originates in its core. This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core. The motion of the liquid in the outer core is driven by heat flow from the inner core, which is about 6,000 K (5,730 °C; 10,340 °F), to the core-mantle boundary, which is about 3,800 K (3,530 °C; 6,380 °F). The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core.

The mechanism by which the Earth generates a magnetic field is known as a dynamo.

(Wikipedia)

The Dynamo Effect

The simple question “how does the Earth get its magnetic field?” does not have a simple answer. It does seem clear that the generation of the magnetic field is linked to the rotation of the earth, since Venus with a similar iron-core composition but a 243 Earth-day rotation period does not have a measurable magnetic field. It certainly seems plausible that it depends upon the rotation of the fluid metallic iron which makes up a large portion of the interior, and the rotating conductor model leads to the term “dynamo effect” or “geodynamo”, evoking the image of an electric generator.

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.

 

Refer to this Wikipedia Page and this Hyperphysics page for more details

The GeoMag page is also very informative and useful(Natural Resources Canada)

Gravitational force is the weakest force in nature

Nijisha asked:

why gravitational force is considered as weak force?

Prejith Asked:

What is space time?

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Principles of Physics in Chemistry

Meera Madhu asked:
“is there any priciples of phy involed in chemical reactions ?”
Answer:
Physics and Chemistry are the two main branches of Physical Science, the branch of science which discusses nature and its properties and the various phenomena associated with it.
Some of the Principles to mention are
The Principles of conservation,
Thermal expansion
How to hold a test tube, pipette, Burette etc?
(Visitors are requested to add more)

Nature of light, relativity and blackholes

Prasanna asked:

we know light has got dual nature. & blackholes has got enormous gravity from which even light cant escape. how can gravity can influence a mass less stream of particles like gravity?

Ans:

Do you know why solar eclipse is watched with great importance by the scientific community?

OK

Einstein’s theory of General Relativity was proved right(?) when bending of light by masses was observed in reality.

Please go through the links below and hope that you’ll find an answer there.

http://en.wikipedia.org/wiki/General_relativity

http://www.suite101.com/

Mass of Proton

Anshul asks:

“how can we say that charge and mass of a proton has a constant value if it depends on the nature of the gas taken”

Answer: The mass of proton does not depend on the nature of gas or material.

How does light travel?

Akashjot Kaur asks

“how a wave travels ? eg. light has dual nature ,since  light consists of particles ,and in the wave character we say it moves in the form of electric & magnetic perpendicular wave.how is it possible? it travels in the form of waves or particles?”

Answer to be posted soon

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