Displacement
is a vector quantity as it is associated with direction,but distance is
a scalar quantity which does not give any information about direction
of motion.Distance and displacement magnitude are numerically equal only
when the body travels in a straight line from A to B(i.e the shortest
distance from a point to another). Also distance has always a non-zero
magnitude,but displacement can be zero if the body returns to the point
of origin at the end of motion.
Why do we hear a hissing sound when we open a Thumsup/Coke bottle?
The Coke is pumped with CO2 gas for
carbonation process. Coke sealed under pressure condition. Partial gas gets
dissolved in the liquid as bubbles and the remaining occupy the volume at the surface
of the liquid and sealed cap. When the bottle is opened due to pressure
difference, there is rush of gas at liquid surface to outside the bottle followed
by dissolved gas rushing out from liquid making small explosions of liquid at
surface leading to hissing sound and bubbles.
What is Carbon dating?
Radioactive C-14 is produced in our atmosphere by the bombardment of N-14 by neutrons produced by cosmic rays. The radioactive carbon-14 combines with oxygen to form carbon dioxide and is incorporated into the cycle of living things.
Carbon-14 decays with a half life of about 5730 years by the emission of an electron of energy 0.016 MeV. This changes the atomic number of the nucleus to 7, producing a nucleus of nitrogen-14. At equilibrium with the atmosphere, a gram of carbon shows an activity of about 15 decays per minute.
Presuming the rate of production of
carbon-14 to be constant, the activity of a sample can be directly compared to
the equilibrium activity of living matter and the age calculated.
FACE CENTERED CUBIC STRUCTURE
Atoms touch each other along face diagonals. All atoms are
identical; the face-centered atoms are shaded differently only for ease of
viewing.
ex: Al, Cu, Au, Pb, Ni, Pt, Ag
Coordination no = 12
4 atoms/unit cell: 6 face x 1/2 + 8 corners x 1/8
Atomic Packing Factor for a face-centered cubic structure =
0.74
Close-packed directions: length = 4R = sqrt (2a)
Unit cell contains: 6 x 1/2 + 8 x 1/8 = 4 atoms/unit cell
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