Question

dimensionless physical constant

Answer 1

Dimensionless fundamental physical constants include: α, the fine structure constant, the coupling constant for the electromagnetic interaction.

Answer 2

Dimensionless fundamental physical constants include: α, the fine structure constant, the coupling constant for the electromagnetic interaction (≈​1⁄137). Also the square of the electron charge, expressed in Planck units, which defines the scale of charge of elementary particles with charge.