Can variables be dimensionless ?

A dimensionless quantity

A dimensionless quantity

What are (i) dimensional constant, (ii) dimensionless constants, (iii) dimensional variables and (iv) dimensionless variables.

A : Absolut error is unitless and dimensionless. R : All type of errors are unitless and dimensionless.

A : Displacement gradient is a dimensionless quantity. R : Displacement is dimensionless quantity.

Assertion : Emissivity of any body (e) is always less than its absorptive power (a). Reason : Both the quantities are dimensionless.

What are dimensionless variables? Why are they called so?

A : A unitless physical quantity must be dimensionless. R : A pure number is always dimensionless.

Which one of the following is not the dimensionless quantity?

g is dimensional constant where as pi is the dimensionless constant. Why?