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What is impact parameter?

Impact parameter is the perpendicular distance between the velocity vectors of two objects (considered to take part in a collision) when they are at infinite distance (at such a distance that there is no interaction between the two particles)

In Rutherford’s alpha scattering experiment, the gold nucleus is at rest and therefore, in this case

Impact parameter is the perpendicular distance between the gold nucleus and the the direction of the velocity vector of alpha particle when the alpha particle is at infinite distance (i.e; the force of interaction between the gold nucleus and the alpha particle is negligibly small)

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.

Recent Research Publications in Physics

Mass of Neutrino

The absolute scale of neutrino masses is very important for understanding the evolution and the structure formation of the Universe as well as for nuclear and particle physics beyond the present standard model.

Elastic Scattering of He at the surface of liquid helium

Elastic scattering of 4He atoms when they approach the surface of 4He liquid, has been studied. The liquid surface is assumed to be uniform and the density profile is the same along and perpendicular to the surface. The incident 4He atom will interact with a large number of 4He atoms in the liquid near the surface of liquid 4He. Hence, the effective interaction of the incident particle will be due to many-body forces.

Is linear momentum conserved when a ball is thrown vertically up in the sky?

ROUNAK BHATTACHARJEE asked the above question.

The fact is that linear momentum is conserved in all interactions. If you concentrate on the motion of a single body alone, that will not account for an interaction. When thrown above, according to the principle of conservation of momentum, what we can say is that “The total momentum of the ball plus the thrower just before throwing is equal to the total momentum just after throwing”

After that what happens is controlled by the force of gravity acting on it. The force acting on it can change the momentum. Here the interaction is between the ball and the earth. On account of the huge mass of earth, the motion of earth to compensate the motion of ball and to conserve the momentum cannot be detected.

However, the linear momentum is conserved in all events and interactions so far!

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