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Fine Structure Constant

Please tell me what is fine structure constant? (Asked Deepanshu Gabba )

Answer:

A fundamental and dimensionless physical constant, equal to approximately 1/137, that occurs in expressions describing the fine structure of atomic spectra

In physics, the fine-structure constant (usually denoted α, the Greek letter alpha) is a fundamental physical constant, namely the coupling constant characterizing the strength of the electromagnetic interaction.

HYSTERISIS

Namrata Asked:

What is hysteresis? I only know its related to the frequency.

 

Ans:

Hysterisis mens “Lagging Behind”

 

Hysteresis phenomena occur in magnetic materials, (as well as in the elastic, electric, and magnetic behavior of materials,) in which a lag occurs between the application and the removal of a field (or force) and its subsequent effect

The lack of retraceability of the magnetization curve is the property called hysteresis

 

Magnetic hysteresis

When an external magnetic field is applied to a ferromagnetic substance, the atomic dipoles align themselves with the external field. Even when the external field is removed, part of the alignment will be retained: the material has become magnetized.

The relationship between magnetic field strength (H)(EXTERNAL) and magnetic flux density (B) (ACQUIRED) is not linear in such materials. If the relationship between the two is plotted for increasing levels of field strength, it will follow a curve up to a point where further increases in magnetic field strength will result in no further change in flux density. This condition is called magnetic saturation.

If the magnetic field is now reduced linearly, the plotted relationship will follow a different curve back towards zero field strength at which point it will be offset from the original curve by an amount called the remanent flux density or remanence (RETENTIVITY).

If this relationship is plotted for all strengths of applied magnetic field the result is a sort of S- shaped loop. (See the diagram) The ‘thickness’ of the middle bit of the S describes the amount of hysteresis, related to the coercivity of the material.

A Question from Magnetic Effects of Current

Gavin Pinto asked

“A current carrying wire is placed above a magnetic needle. What do you observe? If you want to increase this effect, what will you do? If you want to reverse the effect, what will you do?”

 

Ans: When a current carrying conductor is placed above a magnetic needle, the magnetic needle is deflected and tends to align itself perpendicular to the conductor. The effect can be increased by increasing the strength of current through the wire or by decreasing the distance.

However, the maximum deflection which can be produced is 90 degree, when the magnetic field produced by the current carrying wire is very much greater than the earth’s magnetic field.

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