Question

Name the physical quantity which has unit but no dimesion

Answer 1

In dimensional analysis, a dimensionless quantity (or more precisely, a quantity with the dimensions of 1) is a quantity without any physical units and thus a pure number. Such a number is typically defined as a product or ratio of quantities which do have units, in such a way that all the units cancel out. Numerous well-known quantities, such as pi, e are dimensionless. By contrast, non-dimensionless quantities are measured in units of length, area, time, etc. Examples of dimensionless physical quantities are decibel, entropy (in the meaning of the log of number of states), drag coefficient, coefficient of kinetic friction etc.