20.1  Electric Charge and Static Electricity (continued)

Electric Charge

Recall that electrical energy is the energy associated with electric charges. But what exactly is electric charge? Electric charge is a property that causes subatomic particles such as protons and electrons to attract or repel each other. There are two types of electric charge, positive and negative. Protons have a positive charge and electrons have a negative charge. Electric charges move in a flash through a lightning bolt. Electric charges attract one another in clothes taken from the dryer. Although charged particles are too small to see, just about everything in your daily life is affected by charge in one way or another.

Figure 2 shows how charges are arranged in an atom. A cloud of negatively charged electrons surrounds the positively charged nucleus. The atom is neutral because it has an equal number of positive and negative charges. If an atom gains one or more electrons, it becomes a negatively charged ion. If an atom loses electrons, it becomes a positively charged ion.   An excess or shortage of electrons produces a net electric charge.

Figure 2  A neutral atom has equal numbers of protons and electrons.

The SI unit of electric charge is the coulomb (C). It takes about 6.24 × 10¹⁸ electrons to produce a single coulomb. A lightning bolt is about 10 to 20 coulombs of charge. In comparison, a flash camera uses the energy from 0.025 coulombs of charge to produce each flash.