ABSTRACT
The electric force law is similar, in many ways, to Newton’s law of gravity. It is given by the equation
F = Kq1q2/d2 (5.1)
where q1 and q2 are electric charges that are measured in units of coulombs. There are two different types of charges, positive and negative. The unit of charge is named after Charles Coulomb, who rst wrote down Equation 5.1, which is, in fact, known as Coulomb’s law. Charge is a fundamental property of matter. It is independent of the other fundamental properties of mass, length, and time. Thus, the coulomb is a fundamental unit, not expressible in terms of the other units. The charge of the electron or proton, which is the smallest observed charge, is 1.6 × 10−19 coulombs. Some of you may have heard about quarks, which are believed to be the basic building blocks of matter (protons are made up of three of them) and have one-third or two-thirds the charge of the electron. But free quarks are never observed directly, so the statement above about the smallest observed charge is still true. We will discuss quarks and other basic building blocks in a later chapter.
