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Answer:
Explanation:
Assume a point sound source that emits a sound power<em> P </em>(in W) evenly in all directions of space. Let us also assume that the medium does not absorb this sound power when it passes through it. At a distance<em> d </em>from the source this power will have been evenly distributed over the surface of a sphere of radius <em>d</em>. Therefore, the acoustic intensity I at distance d will be worth:
This is the expression of the so-called<em> law of the square of distance: "the intensity is inversely proportional to the square of the distance to the source (considered punctual)".</em>
So
In physical chemistry, the terms body-centered cubic (BCC) and face-centered cubic (FCC) refer to the cubic crystal system of a solid. Each solid is made up simple building blocks called lattice units. There are different layouts of a lattice unit.
It is better understood using 3-D models shown in the picture. A BCC unit cell has one lattice point in the center, together with eight corner atoms which represents 1/8 of an atom. Therefore, there are 1+ 8(1/8) = 2 atoms in a BCC unit cell. On the other hand, a FCC unit cell is composed of half of an atom in each of its faces and 1/8 of an atom in its corners. Therefore, there are (1/2)6 + (1/8)8 = 4 atoms in a FCC unit cell.
It is better understood using 3-D models shown in the picture. A BCC unit cell has one lattice point in the center, together with eight corner atoms which represents 1/8 of an atom. Therefore, there are 1+ 8(1/8) = 2 atoms in a BCC unit cell. On the other hand, a FCC unit cell is composed of half of an atom in each of its faces and 1/8 of an atom in its corners. Therefore, there are (1/2)6 + (1/8)8 = 4 atoms in a FCC unit cell.