Which of the following is a dimensionless quantity?
Show Hint
The expression for the optical density is given by-
Log10 (1/T), where T is the transmittance. From this the dimensional formula can be deduced.
- Magnetic flux density
- Electric flux density
- Lumen flux density
Optical density
The Correct Option is D
Solution and Explanation
Optical density is the ratio of the speed of light in two media. Whenever light passes through an optically dense medium, it bends towards the normal. The extent to which it bends is measured as the optical density of the medium. As optical density is the ratio of two same physical quantities, therefore it has no unit. Hence, optical density is a dimensionless quantity.
The other 3 quantities mentioned in the options above have a specific unit and thus have dimensions.
- Magnetic Flux Density - It is the force acting per unit current per unit length on a wire placed under magnetic field. Its SI unit is Tesla.
- Electric Flux Density - It is the measure of the intensity of electric field generated by an electric charge. Its SI unit is NC-1.
- Lumen Flux Density - It is a measure of the intensity of light passing through a unit section per unit time. Luminous flux is measured in Lumens.
Also Read: Ray Optics & Optical Instruments
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Concepts Used:
Physical World
The physical world includes the complications of the natural world around us. It is a type of analysis of the physical world around us to understand how it works. The fundamental forces that control nature are:
- Gravitational Force is a universal force that exists as an outcome of mutual attraction between any two objects with respect to their masses.
- Electromagnetic Force can be understood as the force that is present between the charged particles. The force is stated by Coulomb’s law.
- Strong Nuclear Force is the force that ties the protons and neutrons in a nucleus. Of all the elemental forces in nature, a strong nuclear force is the strongest as its name suggests.
- Weak Nuclear Force can only be noticed in some of the nuclear processes such as the beta decay of the nucleus.