Physical World Units And Measurements Ques 20
20. Which of the following is a dimensional constant?
[1995]
(a) Refractive index
(b) Poissons ratio
(c) Relative density
(d) Gravitational constant
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Answer:
Correct Answer: 20.(d)
Solution:
- (d) A quantity which has dimensions and a constant value is called dimensional constant. Therefore, gravitational constant (G) is a dimensional constant.
Value of $G=6.67 \times 10^{-}$ ${ }^{11} m^{2} / kg / sec^{2}$
dimension of $G=[M^{-1} L^{3} T^{-2}]$
Relative density, refractive index and poisson ratio all the three are ratios, therefore they are dimensionless constants.
Angle is an exceptional physical quantity, which though is a ratio of two similar physical quantities $($ angle $=\frac{\text{ arc }}{\text{ radius }})$ but still requires a unit but no dimensions.
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