Fine structure constant is a fundamental physical constant proposed by Sir Arthur Eddington in 1916. It defines the strength of electromagnetic interaction between the two elementary charged particles. It is denoted by the letter α and its also called as Sommerfeld's constant. As its a dimensionless constant, it has same numerical value in all system of units.

Fine structure constant is a fundamental physical constant proposed by Sir Arthur Eddington in 1916. It defines the strength of electromagnetic interaction between the two elementary charged particles. It is denoted by the letter α and its also called as Sommerfeld's constant. As its a dimensionless constant, it has same numerical value in all system of units.