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# Conceptual Objective1: Electric charges

• 1.1: Overview
Atoms contain negatively charged electrons and positively charged protons; the number of each determines the atom’s net charge.
• 1.2: Shelding and Charging Through Induction
Electrostatic shielding is the phenomenon that occurs when a Faraday cage blocks the effects of an electric field.
• 1.3: Prelude to Electric Charges and Fields
Back when we were studying Newton’s laws, we identified several physical phenomena as forces. We did so based on the effect they had on a physical object: Specifically, they caused the object to accelerate. Later, when we studied impulse and momentum, we expanded this idea to identify a force as any physical phenomenon that changed the momentum of an object. In either case, the result is the same: We recognize a force by the effect that it has on an object.
• 1.4: Electric Charge
You are certainly familiar with electronic devices that you activate with the click of a switch, from computers to cell phones to television. And you have certainly seen electricity in a flash of lightning during a heavy thunderstorm. But you have also most likely experienced electrical effects in other ways, maybe without realizing that an electric force was involved. Let’s take a look at some of these activities and see what we can learn from them about electric charges and forces.
• 1.5: Conductors, Insulators, and Charging by Induction
In the preceding section, we said that scientists were able to create electric charge only on nonmetallic materials and never on metals. To understand why this is the case, you have to understand more about the nature and structure of atoms. In this section, we discuss how and why electric charges do—or do not—move through materials. A more complete description is given in a later chapter.