Introduction to Specific gravity value
Relative density or specific density value of a substance is the ratio of the substance density to the density of water. Since its the ratio, specific gravity of a substance is a unit-less quantity. It is defined so that the value remains same even when we use different system of units such as ft-lb.
Examples of Specific Gravity Value
An liquid substance has a mass of 11.5 g and occupies a volume of 13.4 ml. Find the density of the liquid substance.
The density can be calculated as
? = [(11.5 g) / (1000 g/kg)] / [(13.4 ml) / (1000 ml/l) (1000 l/m3) ]
= (11.5 10-3 kg) / (13.4 10-6 m3)
= 858.20 kg/m3
The Specific Gravity value or relative density value is a dimensionless number defined as the ratio of density of the material to the density of water at a certain temperature.
Specific Gravity value can be expressed as
SGV = = ? / ?H2O (3)
SGV = specific gravity value
? = density of fluid or substance (kg/m3)
?H2O = density of water (kg/m3)
It is common to use the density of water at 4 oC (39oF) as reference as the density of water is at the highest at this temperature- 1000 kg/m3 or 62.4 lb/ft3.
If the density of iron is 7850 kg/m3,what is the specific gravity of iron ?
SG = (7850 kg/m3) / (1000 kg/m3)
Specific Gravity Values : Table
Specifice gravity values of some common substance are given below
8.4 – 8.7
Chromium dioxide (Cr203)
Chromium oxide (Cr02)
4900 kg m-3
8.8 – 8.95
Copper ore, pyrites
4.1 – 4.3
Flint stones/ pebbles
2.4 – 2.6
19.25 – 19.35
21.78 – 22.65
Iron, gray cast
7.03 – 7.13
Iron, cast, pig
7.6 – 7.9
Iron ore, hematite
Iron, ore, limonite
3.6 – 4.0
Iron ore, magnetite
4.9 – 5.2
Iron ore, specular
2.5 – 3.0
Lead ore, galena
7.3 – 7.6
Lead oxide (yellow)
9.5 – 9.9
Manganese ore, pyrolusite
3.7 – 4.6
Monel metal, rolled
10.4 – 10.6
2.6 – 2.7
Steel, 440C stainless
7.70 – 7.73
7.2 – 7.5
Tin ore, cassiterite
6.4 – 7.0
Laser: An artificial light source which has many features is laser. When a light is exposed into a medium , there are three processes can happen and have struggle with the medium.
In emission process the atoms have a movement from the excited state to the ground state where as in absorption process the movement of atom is from the ground state to the absorption state.
In this process of spontaneous emission the atoms in the state of excited state E2 returns to the lower state of ground state. That is the atom moves from the higher state to lower state. It is happening by emitting the photon having an energy hv with out the need of external action.
Spontaneous emission is defined as the emission of radiation which is not due to any external force.
Representation of spontaneous emission:
This spontaneous emission is considered as an uncontrollable and random process.
Stimulated emission and absorption:
Stimulated emission is same as the spontaneous emission but it is happening due to some force.
In this there is a connection among the atom in excited state and the photon. The photon can trigger an atom, to move from excited state to the ground state E1. This movement can form a new photon similar to the old photon such as frequency, phase, direction and propagation. In laser performance stimulated process is act as a key factor.
Representation of stimulated factor:
As in figure before emission there is only one photon and the atom is in excited state E2. During stimulation the photon can trigger an atom and transfer it to the lower ground state E1. This process is otherwise known as induced emission.
Stimulated emission is more powerful because it can be multiplied by a chain reaction and leads to the coherent.
Stimulated absorption is the reverse process of stimulated emission. In this an atom in the ground state E1 absorb a photon of energy hv and goes to the excited state E2. An energy of the photon is equivalent to E2 – E1.
As in figure after absorption of photon the atom moves from ground state to excited state.
Titanium dioxide, Anatase
Tin, 100% Pure
6.9 – 7.2
Zinc, ore, blend
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