Electric charge is quantized. Elementary charge (charge of electron)
Direction of the electric force is always along the line joining the two objects. Direction of the force depends on whether the charges have the same sign or opposite sign.
Coulomb’s Law in terms of e 0, permittivity of free space.
Conceptual Example Two positive point charges Q 1 =50 m C and Q 2 =1 m C, are separated by a distance l. Which is larger in magnitude, the force that exerts on Q 1 exerts on Q 2, or the force that Q 2 exerts on Q 1 ?
1.A handheld glass can be charged by rubbing it with silk or a plastic bag while holding it in your hands. Would you conclude from this that glass is a conductor or an insulator? Why? 2.Why it is easier to charge a balloon on a dry day than on a humid day? 3.Why are neutral objects attracted to both negatively and positively charged objects?
1.When Coulomb was developing his law, he did not have an instrument for measuring charge. And yet he was able to obtain spheres with ½ ; 1/3; ¼;… of some original charge. How might he have used a set of identical spheres to do this? 2.You have three identical metal spheres on insulating stands. The spheres hold charges Q A = -2q; Q B = -q; Q C =4q. First, sphere A is brought into contact with sphere C and separated. Second, sphere C is brought into contact with sphere B and separated. What is the resulting charge on sphere B?