The concept of unit charge can be cleared easily from equation 1.3. Lets suppose r=1m, q1=q2=q and the force F=9 X 10 9.
By substititing the values in equation 3 we get:
So, S.I. unit of charge is Coulomb.
Conclusion: When two charges of 1 coulomb each are placed at a separation distance of near about 1 meter, then the charges will repel each other by a force of 9 X 10 9 coulomb.
Unit of charge in c.g.s system is 1 electrostatic unit(e.s.u) or stat coulomb.
Charge on electron in terms of stat coulomb is 4.8 X 10 -10.
1.602 X 10 -19 coulomb = 4.8 X 10 -10stat coulomb
= 3 X 10 9stat coulomb